Business energy back-billing rules: does the 12-month limit protect your company?

A business does not automatically have to pay every historic energy charge that a supplier discovers.

In Great Britain, Ofgem’s back-billing rules normally prevent a supplier from recovering previously unbilled gas or electricity charges that are more than 12 months old from a qualifying microbusiness, provided the customer did not behave obstructively or in a manifestly unreasonable way.

However, the protection does not apply to every company. It does not generally stop collection of a charge that was billed correctly and on time but left unpaid, and it is not an automatic 12-month limit for larger businesses.

The practical answer therefore depends on four questions:

1. Was the customer a microbusiness for the relevant supply?
2. Is this genuinely a new catch-up charge rather than an old unpaid bill?
3. Which consumption and supply charges fall more than 12 months before the supplier’s recovery action?
4. Did the customer’s conduct prevent the supplier from billing correctly?

This guide explains the rules in England, Scotland and Wales, the separate 13-month position in Northern Ireland, how to test a supplier’s calculation and how to dispute an ineligible back bill.

Rules and complaint routes last reviewed: 7 August 2026. This guide provides general information rather than legal advice on an individual contract or debt.

Business energy back-billing at a glance

Question	Short answer
Is there a 12-month limit?	Yes, in Great Britain for domestic customers and qualifying microbusiness consumers in the circumstances covered by Ofgem’s rules
Does it protect every business?	No. A business that is only within the newer “Small Business” category is not automatically protected by the 12-month licence condition
What does the limit cover?	Previously unbilled or underbilled energy, standing charges and other supply charges relating to more than 12 months before charge recovery action
Does it cancel all debt older than 12 months?	No. A supplier can continue pursuing a valid bill that it originally issued in compliance with the rule
Do estimated bills defeat protection?	Not by themselves. Ofgem says customers should not be blamed merely for failing to spot estimates or submit readings
Does it cover a Direct Debit set too low?	It can. Ofgem expressly identifies incorrect Direct Debit levels as a back-billing scenario
Does it cover smart and half-hourly meters?	Yes. The rule is not restricted by meter type, payment method or metering arrangement
Can customer conduct remove protection?	Yes, where obstructive or manifestly unreasonable behaviour prevented accurate billing; theft, tampering and preventing physical meter access are key examples
What is the Northern Ireland limit?	13 months for qualifying domestic and microbusiness customers, under separate Utility Regulator rules
Who can use the Energy Ombudsman?	Eligible microbusinesses and small businesses can normally escalate after eight weeks or a deadlock letter

The official starting points are Ofgem’s back-bill guidance and its detailed SLC 21BA compliance guidance.

What is a business energy back bill?

A back bill is a demand for energy or supply charges that were not billed accurately at the proper time.

It may be described as:

• A catch-up bill
• A rebill
• A reconciliation
• A corrected invoice
• An account adjustment
• A retrospective charge
• An unbilled-consumption invoice
• A balance brought forward

The label is not decisive. The important issue is what the supplier is now trying to recover and whether it demanded the same charge before.

Common causes include:

• No bills being issued for a period
• Bills based on estimates that were too low
• Actual meter readings not being processed
• A wrong meter serial number being linked to the account
• An incorrect electricity meter multiplier
• A meter exchange not being updated
• A faulty or incorrectly configured meter
• A smart meter communication problem
• Missing or rejected half-hourly data
• The wrong tariff or unit rate being applied
• A Direct Debit being set below the cost of consumption
• A change of tenancy being recorded late
• The supplier registering the wrong MPAN or MPRN
• An industry data or settlement correction

Read the corrected invoice alongside the original bills. A document headed “rebill” may contain both charges that were already billed and a newly added shortfall. Only the genuinely new recovery needs to be tested under the back-billing rule.

What does Ofgem’s 12-month rule say?

Standard Licence Condition 21BA governs back-billing by licensed gas and electricity suppliers in Great Britain.

In simplified terms, when a supplier issues a bill or otherwise seeks payment, it should recover only:

• Units of gas or electricity reasonably considered to have been consumed during the 12 months before that recovery action; and
• Standing charges or other supply charges accrued during that same 12-month period.

Ofgem calls the bill, demand or other collection step a charge recovery action.

The rule first applied from 1 May 2018. Ofgem’s licence-modification decision explains that the condition was introduced to protect consumers from lengthy catch-up bills.

The detailed wording matters because the rule is not simply:

Any balance more than 12 months old disappears.

Instead, it limits the age of previously unbilled supply charges that can be included when recovery action is first taken, subject to stated exceptions.

Who does the 12-month protection cover?

In Great Britain, SLC 21BA applies to:

• Domestic customers; and
• Microbusiness consumers.

For this article, the important category is the microbusiness consumer. A commercial tariff, company name or business premises does not automatically exclude protection. Equally, calling an organisation a small business in everyday language does not automatically include it.

Current microbusiness criteria

Ofgem’s current business guidance says a business is a microbusiness if it meets either the organisational test or one of the fuel-consumption tests below.

Route	Current Great Britain threshold
Employees and finances	Fewer than 10 employees, or their full-time equivalent, and annual turnover or balance-sheet total of no more than £2 million
Electricity consumption	No more than 100,000kWh of electricity a year
Gas consumption	No more than 293,000kWh of gas a year

These routes are alternatives. A business with more than 10 employees can still qualify for its electricity supply if annual electricity use does not exceed 100,000kWh.

Conversely, a business using more than the electricity threshold may still qualify through the employees-and-finances route.

Ofgem publishes the current thresholds in its guide to getting energy for a business.

A business can qualify for one fuel but not the other

The consumption tests are fuel-specific.

For example, a manufacturer might use:

• 160,000kWh of electricity a year; and
• 240,000kWh of gas a year.

If it does not meet the employees-and-finances test, it may be outside the consumption route for electricity but inside it for gas. A back bill covering both supplies should therefore be assessed separately.

Legal structure does not decide eligibility

The following can potentially qualify if the relevant criteria are met:

• A sole trader
• A partnership
• A limited company
• A charity
• A community organisation
• A club
• A small landlord business
• Another non-domestic customer

The supplier should not reject a claim merely because the account is in a limited company’s name. The relevant size, consumption and contractual status matter more than the legal form.

Ask the supplier to confirm its classification

Where eligibility is close or disputed, ask the supplier to state:

• Whether it treats the customer as a microbusiness
• Which test it applied
• The annual consumption figure and period it used
• The employee and financial information it relied on
• Whether classification differs between gas and electricity
• The contractual and licence basis for refusing SLC 21BA protection

Keep evidence such as annual accounts, payroll headcount, historic invoices and interval-consumption reports. A supplier’s internal account label is relevant evidence, but it should not replace the actual criteria.

Microbusiness is not the same as Small Business

This is the most important trap in the current rules.

Since 19 December 2024, Ofgem has recognised a wider Small Business category for additional non-domestic protections. Its thresholds include businesses with fewer than 50 full-time-equivalent employees and specified financial limits, or annual use of no more than 200,000kWh of electricity or 500,000kWh of gas.

However, the wider Small Business category did not automatically rewrite SLC 21BA. The back-billing condition expressly extends its protection to Micro Business Consumers.

Customer category	12-month back-billing protection under SLC 21BA	Energy Ombudsman access
Microbusiness	Yes, subject to the rule and exceptions	Normally yes
Small Business that is not a microbusiness	Not automatically under SLC 21BA	Normally yes
Medium or large business	Not automatically	Generally outside the business redress scheme

This means a business can be small enough to use the Energy Ombudsman but too large for the automatic 12-month licence protection.

Do not allow the words “small business” and “microbusiness” to be used interchangeably during a dispute. Ask the supplier and Ombudsman to identify the exact regulatory category being applied.

Which charges can the 12-month rule cover?

The licence condition expressly refers to:

• Gas or electricity units
• Standing charges
• Other types of supply charge

Ofgem’s annotated guidance says the condition covers fixed standing charges and variable unit charges. It also applies regardless of payment type.

Potentially affected items can therefore include:

Charge	How to assess it
Unit charges	Allocate consumption to the dates on which it was used and apply the contractual rates for those periods
Standing charges	Count the days falling before and after the 12-month cut-off
Direct Debit shortfall	Identify whether the shortfall represents previously unbilled consumption rather than merely unpaid accurate bills
Pass-through supply charges	Ask how each item relates to the supply period and whether it was previously billed
VAT	Recalculate after any protected underlying charges are removed
Climate Change Levy	Check the taxable quantity and applicable period after adjusting the energy charge
Metering or third-party items	Determine whether they are “supply charges” under the contract and licence condition; standalone service invoices may require separate analysis

Some half-hourly bills contain capacity, meter operator, data collection and network pass-through charges. A supplier should not simply present one aggregated historic figure. Ask it to identify the legal and contractual basis of each component.

The full field-by-field process is covered in our business energy bill guide.

When does the 12-month period start?

The 12 months run backwards from the date of the supplier’s charge recovery action.

That will commonly be the date on which it:

• Issues the catch-up bill
• Sends a demand for the newly identified amount
• Adds the new debt to a prepayment arrangement
• Raises a Direct Debit to recover the historic shortfall
• Otherwise first seeks recovery of the charge

It does not normally run from:

• The date on which the meter fault began
• The date the supplier discovered the error
• The end of the financial year
• The date the customer first complained
• The date a debt collector became involved, where a compliant bill had already been issued

Cut-off example

Suppose a supplier first issues a catch-up bill on 1 August 2026.

The normal 12-month cut-off is 1 August 2025.

For a protected microbusiness that did not cause the problem:

• Newly recovered consumption from 1 August 2025 onwards may normally be billed.
• Newly recovered consumption before 1 August 2025 should normally be excluded.

This does not mean that every invoice dated before the cut-off is ignored. The calculation follows the dates of the underlying consumption and charges, and whether they were previously billed.

How to calculate the protected part of a back bill

Use actual consumption and tariff data wherever possible.

Step 1: identify the first recovery action

Record the date of the first bill or demand that included the newly recovered amount. Keep the PDF, envelope, email header or portal download showing when it was issued.

Step 2: calculate the cut-off

Subtract 12 calendar months from the recovery-action date for a Great Britain microbusiness claim.

Step 3: build a charge timeline

List each billing period with:

• Opening and closing dates
• Opening and closing readings
• Whether each reading was actual, customer, smart, estimated or substituted
• Consumption
• Unit rate
• Standing-charge days
• Other charges
• Original bill date
• Corrected bill date

Step 4: separate old and recent consumption

Split any billing period that crosses the cut-off. Half-hourly or daily data gives the best allocation. Monthly actual readings are the next-best evidence.

Avoid dividing the whole bill evenly by day if use is seasonal or rates changed. A gas site’s winter consumption can be many times its summer use.

Step 5: separate new charges from old debt

Compare every corrected line with earlier invoices. Mark amounts that were:

• Properly billed before
• Paid before
• Credited before
• Newly added now
• Reversed and replaced

Step 6: recalculate tax and payments

After removing any protected supply charges, recalculate VAT, CCL where applicable, payments, credits and the closing balance.

Basic formula

For a straightforward claim:

Revised payable back bill = eligible newly billed charges within 12 months − related payments and credits

The protected amount is:

Protected amount = newly billed charges allocated before the 12-month cut-off

The supplier should provide enough detail for this calculation to be reproduced.

Worked example: three years of previously unbilled electricity

A qualifying microbusiness receives a catch-up invoice on 1 August 2026 covering electricity used from 1 August 2023 to 31 July 2026.

Assume, only for a simple illustration, that the supplier’s schedule attributes £6,000 to each 12-month period:

Period	Illustrative charge	Normal treatment
1 August 2023 to 31 July 2024	£6,000	More than 12 months old; normally protected
1 August 2024 to 31 July 2025	£6,000	More than 12 months old; normally protected
1 August 2025 to 31 July 2026	£6,000	Within the 12-month window; normally recoverable
Total	£18,000	Indicative payable catch-up amount: £6,000

This assumes:

• The customer qualifies as a microbusiness.
• The £18,000 was genuinely unbilled before.
• No relevant exception applies.
• No payment or credit needs to be deducted.
• The rates and consumption were genuinely even.

Real electricity use and tariff rates rarely divide so neatly. The supplier should reconstruct the amount from readings, interval data and the rates in force during each period rather than divide the total evenly by year or day.

Worked example: an old unpaid invoice

A supplier issued an accurate £4,500 invoice in September 2023 for energy used during the previous two months. The microbusiness did not pay it. The supplier continues debt collection in August 2026.

The 12-month rule does not normally write off that debt.

The supplier took charge recovery action when it issued the compliant invoice in 2023. SLC 21BA allows it to continue pursuing the same units and charges later because the problem is non-payment, not previously unbilled consumption.

The business can still dispute:

• Whether the original invoice was actually sent
• Whether it related to the correct premises and account
• Whether the readings and rates were accurate
• Whether payments were omitted
• Whether other contractual or legal time limits apply

But “the bill is now more than 12 months old” is not enough by itself.

Worked example: Small Business but not microbusiness

A company uses 150,000kWh of electricity annually. It has 30 full-time-equivalent employees, £4 million turnover and a £3 million balance sheet.

It falls within Ofgem’s wider Small Business category, but it does not meet:

• The 100,000kWh microbusiness electricity test; or
• The fewer-than-10-employees microbusiness organisational test.

If it receives a three-year electricity correction, the company is not automatically protected by SLC 21BA. It may nevertheless:

• Challenge the accuracy and contractual basis of the rebill
• Rely on any stronger term in its contract or supplier policy
• Argue that the supplier failed applicable standards of conduct
• Use the Energy Ombudsman if it meets the Small Business eligibility rules
• Consider contractual limitation or prescription arguments
• Obtain legal advice where the value is material

This example demonstrates why checking regulatory status must come before calculating a 12-month write-off.

Worked example: incorrect meter multiplier

A microbusiness has a current-transformer electricity meter. The supplier uses multiplier 20 instead of the correct multiplier 40 for four years, even though the metering records and half-hourly data were available.

When the supplier corrects the account, the previously omitted consumption is a potential back bill. Subject to the facts, the company should normally expect SLC 21BA to limit recovery to the 12 months before the first recovery action.

The fact that a meter operator, data collector or industry system contributed to the error does not automatically transfer the whole historic cost to the customer. Ofgem deliberately framed the protection around whether the consumer was at fault, not simply whether the licensed supplier personally caused every error.

The business should obtain:

• Meter technical details
• Current-transformer ratios
• Meter exchange and commissioning records
• Half-hourly consumption files
• Earlier invoices and multipliers
• The supplier’s full rebilling spreadsheet

The customer-fault exception

The 12-month prohibition can be disapplied where the supplier could not recover the correct amount because of the customer’s obstructive or manifestly unreasonable behaviour.

This is a significant exception, but it is not a general duty on the customer to audit the supplier’s work.

Ofgem says the exception is likely to cover situations such as:

• Unlawful conduct
• Meter tampering
• Energy theft
• Preventing physical access to the meter

The exact outcome depends on causation. The supplier should explain how the conduct prevented it from billing the correct amount, not merely show that communication between the parties was imperfect.

Conduct that may put protection at risk

Examples could include:

• Repeatedly refusing reasonable access appointments when the meter could not be read remotely
• Physically blocking or concealing the meter
• Breaking seals or altering metering equipment
• Knowingly interfering with registration of consumption
• Giving deliberately false occupancy or meter information that prevents correct billing
• Ignoring repeated lawful demands for an already issued bill, although that is more likely an old-debt issue than a new back bill

Keep in mind that the supplier carries records of its attempted contacts and access arrangements. A vague statement that the customer “did not engage” should be tested against dates, methods, replies and whether accurate billing was possible by other means.

What Ofgem says is not enough by itself

Ofgem’s annotated SLC 21BA guidance says it is not the policy intention to remove protection simply because a customer:

• Failed to notice that bills were estimated
• Did not report the supplier’s billing error
• Did not identify that debt was accumulating
• Did not respond to requests to submit meter readings

Ofgem also says a failure to provide a meter reading does not by itself absolve the supplier from the 12-month limit.

This is especially important where the supplier had other reasonable routes to obtain or validate data, such as smart readings, half-hourly data, an annual meter visit or metering-agent records.

Estimated bills and meter-reading requests

Estimated bills are one of the most common sources of back-billing disputes.

A sequence of estimates does not automatically mean the customer accepted whatever later correction the supplier raises. Ofgem identifies inaccurate and estimated bills as situations in which the back-billing requirements may apply.

However, customers should still provide readings where safe and reasonably possible. Regular dated readings can:

• Stop an error growing
• Demonstrate the supplier received usable data
• Identify a wrong meter serial number
• Reveal an incorrect multiplier
• Make allocation across the 12-month cut-off more accurate

For every reading, retain:

• A clear meter photograph
• The date and time
• The meter serial number
• Every register shown
• Submission confirmation
• Any supplier response

If the supplier alleges obstruction, ask for its full access log and copies of every request it says was ignored.

Direct Debits set too low

A low Direct Debit does not necessarily mean the customer failed to pay a valid bill.

Suppose a microbusiness paid £300 a month because the supplier set that amount, but actual ongoing charges were £700 a month. If the statements or reconciliations did not accurately demand the true cost, the eventual shortfall may contain back-billed consumption.

Ofgem’s current guidance expressly includes a Direct Debit set too low, and its compliance letter warns suppliers against relying on customers to identify an insufficient monthly payment themselves.

The correct analysis is:

1. What charges were accurately billed at the time?
2. What did the Direct Debit payments cover?
3. What new charges are being added now?
4. Which new charges relate to more than 12 months before recovery action?

A statement showing a growing debit balance may or may not amount to a compliant demand for the underlying charges. Request all statements, invoices and account ledgers rather than relying on the latest balance alone.

Smart, advanced and half-hourly meters

The back-billing protection is not restricted to traditional meters.

Ofgem says the rules apply regardless of:

• Payment method
• Meter mode
• Meter arrangement

That includes disputes involving:

• Smart meters
• Advanced meters
• Half-hourly settled meters
• Prepayment meters
• Traditional credit meters

A smart meter does not create a shorter six-month rule. Nor does it remove the 12-month rule merely because accurate data should have been available.

For a half-hourly site, request the raw interval data in CSV format and compare it with the volumes on the rebill. Check for:

• Missing settlement periods
• Duplicated data
• Estimated or substituted values
• Meter-time changes
• Incorrect multipliers
• Data from the wrong MPAN
• Periods before or after the business occupied the premises

Our guide to half-hourly energy meters explains the underlying data and settlement arrangement.

Wrong meter, MPAN or MPRN

A supplier can bill the wrong supply point or attach the wrong physical meter to an otherwise correct account.

Before accepting a catch-up calculation, compare:

Identifier	What it should match
MPAN	The business electricity supply point
MPRN	The business gas supply point
Meter serial number	The physical meter installed at the premises
Account name	The party responsible during the billed period
Supply address	The actual premises or unit occupied
Opening and closing readings	Dated handover, contract and meter evidence

Use our guides to locate the correct MPAN or MPRN.

If an error caused underbilling, a qualifying microbusiness can still rely on the 12-month rule subject to the normal conditions. If the consumption was not the company’s at all, the stronger argument is that the charge is not its liability, regardless of age.

Change of tenancy and final bills

Back bills frequently arise after a business moves into or leaves commercial premises.

The 12-month rule does not replace the basic question of who was responsible for the supply. A company should not pay for energy used by a previous or later occupier merely because the supplier could not update its records promptly.

Useful evidence includes:

• Signed lease or licence
• Completion statement
• Landlord handover record
• Date keys were collected or returned
• Business-rates records
• Dated opening and closing meter photographs
• Emails notifying the supplier
• Closing and opening invoices
• Companies House or trading-address evidence

Ask the supplier to split the account exactly at the occupancy date and use the documented readings. If no actual handover reading exists, the parties may need a reasonable estimate, but that estimate should be explained.

A delayed final bill can still engage the back-billing protection if the customer was a microbusiness and the supplier first seeks previously unbilled charges more than 12 months later.

Deemed and out-of-contract supplies

A deemed contract commonly arises when a business consumes energy at premises without agreeing a negotiated contract with the incumbent supplier.

SLC 21BA protects qualifying microbusiness consumers; a supplier should not assume that a deemed or out-of-contract tariff removes the licence protection.

The business should still check:

• Which supplier was registered
• When responsibility began
• The published deemed rates for each period
• Standing charges
• Metering and network items
• Whether a negotiated contract later took effect
• Which charges were previously demanded

Deemed rates can be expensive, so the valid recent part of a back bill may still be substantial.

What if a supplier or its administrator sends the bill?

The back-billing condition refers to recovery action by a supplier or its representative. Ofgem has also reminded insolvency practitioners dealing with failed energy suppliers that the requirements apply to charge recovery.

A customer should therefore not accept the argument that the protection disappears simply because:

• The account moved to a debt collector
• A supplier entered administration
• An insolvency practitioner reconstructed the ledger
• Another representative issued the demand

Ask the sender to identify the original bill, the first compliant recovery action and the basis on which it says any exception applies.

The rule does not limit refunds for historic overcharging

SLC 21BA restricts supplier recovery of old, previously unbilled charges. It is not a matching rule that limits customer refunds to 12 months.

Ofgem’s annotated guidance expressly says the licence condition does not prevent a supplier reimbursing a consumer for earlier overcharging, even when it occurred more than 12 months ago.

If a meter multiplier, tariff or reading error caused the business to overpay, request a correction for the full affected period supported by the account records. Separate contractual and statutory time limits may still become relevant, particularly for older claims, so material cases should be reviewed promptly.

The asymmetry is deliberate:

• A protected customer may not be liable for certain old unbilled consumption.
• A supplier cannot use the same back-billing condition as a reason to retain historic overpayments.

What happens to businesses outside the protection?

A company that is not a microbusiness should not assume that a supplier can demand any historic amount without explanation. It simply cannot rely automatically on the 12-month prohibition in SLC 21BA.

It can still examine:

• The express contract terms
• The supplier’s incorporated policies
• Whether the calculation is accurate
• Whether the tariff and pass-through charges were permitted
• Whether notices and invoices were issued as required
• Whether the supplier complied with non-domestic standards of conduct
• Whether an account stated or settlement was agreed
• Whether waiver, estoppel or other legal principles are relevant
• General limitation or prescription periods

Civil time limits are different from back-billing rules

In England and Wales, section 5 of the Limitation Act 1980 generally provides a six-year time limit for an action founded on a simple contract.

In Scotland, section 6 of the Prescription and Limitation (Scotland) Act 1973 provides a five-year prescriptive framework for specified obligations.

These rules are not interchangeable with SLC 21BA. The relevant start date, contract form, acknowledgement, payment, concealment, error and procedural history can change the result. A business should not simply deduct six or five years from the latest invoice and declare the rest void.

Obtain legal advice where an unprotected commercial back bill is large, proceedings are threatened or the relevant dates are disputed.

Northern Ireland uses a 13-month rule

Ofgem regulates the energy market in Great Britain, meaning England, Scotland and Wales. Northern Ireland has a separate regulatory framework.

The Utility Regulator introduced a 13-month back-billing limit for qualifying domestic and microbusiness gas and electricity customers across payment types.

Its published decision defines the covered Northern Ireland microbusiness group for this purpose by annual consumption:

Fuel	Northern Ireland back-billing microbusiness threshold
Electricity	Up to 50MWh, or 50,000kWh, a year
Gas	Up to 73.2MWh, or 73,200kWh, a year

The decision also recognises exceptions where:

• The relevant bill was sent before the condition took effect
• The supplier had already issued the bill and is seeking payment
• Customer conduct was obstructive or manifestly unreasonable

Read the Utility Regulator’s Northern Ireland back-billing decision rather than applying Great Britain’s 12-month threshold and microbusiness definition to an NI account.

Northern Ireland businesses can seek help through the Consumer Council’s business energy service.

Business back-bill date checker

The calculator below identifies the normal Great Britain 12-month cut-off and splits a billing period into older and recent days.

It is a screening tool, not a legal bill calculation. Its optional monetary estimate assumes the charge accrued evenly by day. That can be seriously misleading where consumption is seasonal, tariffs changed or earlier invoices covered part of the amount.

How to check a supplier’s back-bill calculation

Do not begin with the closing balance. Reconstruct the account from the underlying records.

1. Confirm the correct supply point

Match the address, MPAN or MPRN and every meter serial number. Multi-unit buildings and meter exchanges are frequent sources of error.

2. Confirm the responsible customer and dates

Compare the billed period with leases, change-of-tenancy notices and opening or closing readings.

3. Confirm microbusiness status

Apply the relevant current test separately to electricity and gas. Retain evidence supporting the result.

4. Find the first new demand

Identify exactly when the supplier first sought the extra amount. Do not assume the date of the newest reminder is the correct starting point.

5. Obtain a complete account ledger

Ask for all:

• Invoices
• Credit notes
• Statements
• Payments
• Refunds
• Journal entries
• Reversals
• Debt-collection transfers

The opening balance of one invoice is not a sufficient audit trail.

6. Reconcile meter data

Check readings, units, conversion factors and multipliers. For gas, confirm whether the correct volume-correction and calorific-value formula was used. For electricity, check each register and any current-transformer ratio.

7. Check the rates

The supplier should use the contractual rate applicable to each period, including any valid price changes. A historic correction should not simply apply today’s out-of-contract rate to old consumption.

8. Identify the previously billed amount

If old invoices already charged £10,000 and the new reconstruction says the correct figure was £14,000, the potential back-billed amount is ordinarily the £4,000 difference, not all £14,000.

9. Apply the cut-off to the new shortfall

Allocate the difference using actual date-specific data. Separate standing charges and other line items rather than using one percentage for everything.

10. Reconcile VAT, CCL and payments

Finish by recalculating tax and applying every payment and credit once.

Evidence to collect before disputing the bill

Create one chronological evidence bundle containing:

• The catch-up invoice and issue date
• Every earlier invoice and statement
• The supplier’s detailed rebilling calculation
• Contract and renewal documents
• Published deemed-rate sheets where relevant
• MPAN or MPRN
• Meter serial numbers
• Dated meter photographs
• Meter-reading submission receipts
• Smart or half-hourly data
• Meter exchange and test certificates
• Direct Debit notices and bank payments
• Supplier emails and call notes
• Access requests and appointment records
• Lease and change-of-tenancy evidence
• Proof of microbusiness status
• A spreadsheet showing the disputed and undisputed amounts

Name files by date, such as 2026-08-01-catch-up-invoice.pdf. A clean timeline makes the complaint easier for the supplier or Ombudsman to follow.

How to dispute a business energy back bill

Contact the supplier promptly

Write to the supplier’s formal complaints address and state that the message is a complaint. Quote the account, invoice, MPAN or MPRN and disputed amount.

Ask the supplier to:

1. Place the disputed amount on hold while it investigates.
2. Confirm whether it classifies the customer as a microbusiness.
3. Identify the first charge recovery action for every disputed component.
4. Provide the full billing ledger and calculation.
5. Explain why SLC 21BA does or does not apply.
6. Identify any customer-conduct exception relied on and provide evidence.
7. Remove protected charges older than 12 months.
8. Recalculate VAT, CCL, payments and credits.
9. Issue a corrected bill and written outcome.

Pay the undisputed current charges where possible. Stopping all payments can turn a billing dispute into a separate debt and credit-control problem.

Do not rely only on a telephone call

A call can be useful, but follow it with an email recording:

• The date and time
• The adviser and department
• What was agreed
• Any reference number
• The next deadline

Ask for a copy of the call recording if the conversation becomes important evidence.

Request a payment plan for the valid balance

The recent 12-month portion can remain payable even when older charges are removed. If an immediate payment would cause difficulty, propose an affordable schedule based on cash flow.

Do not sign a settlement or acknowledge the entire balance without understanding whether that could affect later arguments. Obtain advice for a large or contentious claim.

Business energy back-billing complaint template

The following wording can be adapted. Replace every bracketed section and attach a schedule of the disputed charges.

Subject: Formal complaint — disputed back bill and SLC 21BA

Account: [account number]
Supply point: [address]
MPAN/MPRN: [number]
Invoice: [invoice number and date]

I am raising a formal complaint about the catch-up charges of £[amount] covering [start date] to [end date].

The customer was a microbusiness consumer for this supply because [state the employee/financial or annual-consumption test and attach evidence].

Your first recovery action for the newly billed amount appears to have been taken on [date]. The normal 12-month cut-off is therefore [date]. Charges relating to consumption or supply before that date appear to be prohibited by Standard Licence Condition 21BA, because they were not billed previously and the customer did not behave obstructively or in a manifestly unreasonable way.

Please place the disputed amount on hold and provide:

1. The complete account ledger, invoices and credit notes.
2. The readings, consumption, rates, multipliers and standing-charge days used.
3. The date and document on which you rely as the first compliant charge recovery action.
4. Your microbusiness classification and calculation.
5. Details and evidence of any SLC 21BA.2 exception you rely on.
6. A revised bill removing protected charges, with VAT, CCL, payments and credits recalculated.

I dispute £[amount] but will [pay/continue paying] the undisputed current charges of £[amount]. Please treat this correspondence under your formal complaints procedure and provide a written final response or deadlock letter if you cannot resolve it.

Yours faithfully,
[name, role and company]

Citizens Advice also provides a general back-billing complaint template.

When can a business use the Energy Ombudsman?

Eligible microbusinesses and Small Businesses can use the Energy Ombudsman for qualifying disputes with participating energy suppliers. The service is free to the complainant.

Under the current route, a complaint can normally be escalated when:

• Eight weeks have passed since the formal complaint was raised without resolution; or
• The supplier issues a deadlock letter sooner.

Ofgem’s current guidance on business energy contracts and disputes confirms that micro and small businesses can seek resolution through the Energy Ombudsman. The Energy Ombudsman’s business eligibility guidance confirms the current eight-week or deadlock route.

The Ombudsman can require action such as:

• Correcting the account
• Issuing a revised bill
• Providing an explanation
• Apologising
• Paying an award where appropriate

The supplier is bound if the customer accepts the Ombudsman’s decision. Preserve the supplier complaint date and any deadlock letter, and submit within the Ombudsman’s applicable time limit.

Billing is not a niche complaint. The Energy Ombudsman’s 2025 annual data, published in March 2026, says billing disputes represented 56% of the cases it received and identifies 3,216 back-billing cases during the year.

Medium and large businesses are generally outside this consumer redress route. Their unresolved disputes may require negotiation, expert determination, arbitration or court proceedings, depending on the contract.

What outcome should the business request?

Be specific. A useful requested resolution might include:

• Written confirmation of microbusiness status
• Removal of all newly recovered charges before the cut-off
• A line-by-line revised invoice
• Reversal of associated VAT and CCL
• Correct allocation of payments and credits
• Suspension of collection activity on the disputed amount
• Removal of incorrect late-payment charges
• Correction of adverse credit reporting caused by the disputed bill
• A reasonable payment plan for the valid recent balance
• Compensation or a goodwill award where service failures caused material inconvenience
• Confirmation that meter and account records have been corrected

Avoid asking only for the bill to be “looked at”. Define the arithmetic and records needed to close the complaint.

Common supplier arguments to examine

“You should have noticed the low bills”

Ofgem says customers must not be held responsible merely for failing to identify billing errors or an accumulating balance. This argument alone should not defeat protection.

“You did not send readings”

A failure to provide readings does not automatically remove the limit. Ask what other steps the supplier took and how the omission actually prevented accurate billing.

“We sent estimates, so you were billed”

An estimated invoice may bill part of the consumption, but a later shortfall can still be newly recovered. Compare the original amount with the rebill and apply the rule to the difference.

“The error was caused by the meter operator or data collector”

The regulatory protection is not confined to errors made solely inside the supplier. Ask why a third-party or system failure should alter the customer-not-at-fault analysis.

“It is a business account, so the rule does not apply”

The rule expressly applies to microbusiness consumers. Provide the qualifying evidence and ask for the refusal in writing.

“Your company is a Small Business”

That answer is incomplete. Ask whether it is also a microbusiness. The categories overlap but are not identical.

“The debt is older than 12 months but was already billed”

This may be a valid distinction. Ask for the original compliant invoice and proof of when and how it was issued. If it exists, the dispute may concern old debt rather than back-billing.

“Our contract permits retrospective reconciliation”

A supplier cannot enforce a contract term incompatibly with SLC 21BA against a protected microbusiness. For a larger company, the reconciliation wording may be more important and should be reviewed carefully.

How to reduce future back-billing risk

Even where the licence provides protection, preventing the problem is better than litigating the cut-off.

Review every invoice

Check:

• Supply address
• MPAN or MPRN
• Meter serial number
• Reading type
• Opening and closing readings
• Multiplier
• Unit rate
• Standing-charge days
• Contract dates
• Payments and credits

Record regular readings

Take dated photographs monthly, including the meter serial number and every register.

Download interval data

Half-hourly businesses should retain local copies rather than depending indefinitely on one supplier portal.

Reconcile Direct Debits

Compare payments with actual invoiced charges. A low payment can conceal an accumulating liability even if older catch-up charges may later be protected.

Check meter exchanges

Record the removed meter’s final reading and the new meter’s opening reading, serial number, multiplier and installation date.

Notify occupancy changes immediately

Send the supplier the legal entity, responsibility date, lease evidence and dated reading. Request written confirmation.

Keep records for the life of the dispute

Supplier portals can remove old invoices after a switch or account closure. Download bills, contracts and data regularly.

Frequently asked questions

Business energy back-billing checklist

Before accepting or disputing a catch-up invoice, confirm:

1. The supply is in England, Scotland or Wales; if it is in Northern Ireland, apply the separate 13-month rules.
2. The responsible entity and occupancy dates are correct.
3. The MPAN or MPRN matches the premises.
4. Every meter serial number matches the installed or historic meter.
5. Microbusiness status has been tested separately for each fuel.
6. The supplier has identified the first charge recovery action.
7. The 12-month cut-off has been calculated from that date.
8. Previously billed amounts have been separated from new charges.
9. Old unpaid debt has not been confused with unbilled consumption.
10. Consumption has been allocated using actual or interval data where available.
11. Estimated readings and substitution methods are explained.
12. Multipliers, conversion factors and registers are correct.
13. Contract rates have been applied to the right periods.
14. Standing charges have been split at the cut-off.
15. Other supply charges have been itemised.
16. VAT and CCL have been recalculated.
17. All payments, refunds and credits are present.
18. Any allegation of obstruction is supported by dated evidence and causally linked to the billing failure.
19. The undisputed amount has been identified.
20. The complaint was submitted formally and its start date recorded.
21. An Ombudsman deadline or legal deadline will not be missed.

Final verdict

The 12-month business energy back-billing limit offers strong protection, but only when the correct customer and charge fall within it.

In Great Britain, a qualifying microbusiness should not normally be required to pay newly recovered gas, electricity, standing or other supply charges relating to more than 12 months before the supplier’s recovery action when the customer did not prevent accurate billing.

The protection is not a blanket rule for every company. It does not automatically cover a Small Business that falls outside the microbusiness definition, and it does not erase a bill that was correctly issued but simply remained unpaid.

The most reliable approach is to establish microbusiness status, identify the first demand, reconstruct the underlying consumption and split genuinely new charges at the calendar cut-off. If the supplier will not correct an eligible bill, raise a formal complaint and use the Energy Ombudsman where the business qualifies.

For Northern Ireland, apply the separate 13-month rule and thresholds rather than Ofgem’s Great Britain framework.