What the back-billing rule actually says
The most useful piece of consumer protection in UK energy is also one of the least well known. Standard Licence Condition 21BA (for domestic customers) and Standard Licence Condition 7A (for microbusinesses) prevent a licensed gas or electricity supplier from recovering charges for energy used more than 12 months ago, where the supplier was at fault for not having billed accurately within that period. The rule has been in force since 1 May 2018 and applies to every supplier holding an Ofgem retail licence.
The wording matters. The clock is anchored on the date of accurate billing, not the date the meter was read or the date the customer first received correspondence. A supplier that has issued estimated bill after estimated bill and then suddenly produces a "true-up" charge for two years of unbilled consumption has, in nearly every case, lost the ability to recover the portion of that charge that relates to consumption more than twelve months before the corrected bill.
When the 12-month clock starts
The rule cannot be applied retrospectively to consumption that has already been correctly billed. What it does is cap the supplier's ability to back-bill — to recover charges for periods that should have been billed at the time but were not.
The trigger events that start the 12-month protection running are:
- The customer receives a corrected bill that materially differs from previous bills for the same period.
- The supplier admits, in writing, that earlier billing was inaccurate.
- The supplier issues a bill following a previously-ignored meter read or a discovered system error.
From any of those trigger points, the supplier may only recover charges that relate to the 12 months immediately preceding the trigger. Consumption older than that is, in regulatory terms, written off.
The four evidence categories suppliers actually respond to
In our casework the strongest claims share one or more of four evidence categories. Suppliers settle quickly when at least one is present and well documented; they push back hard when the case rests on assertion alone.
- Ignored meter reads. The customer (or a meter reader on the supplier's behalf) submitted accurate reads which the supplier then failed to bill on. The reads can be evidenced from online accounts, email confirmations, or the meter's own register where the supplier later acknowledges the readings exist.
- Demonstrable system error. The supplier's billing system rejected reads, double-counted consumption, applied the wrong tariff, or assigned consumption to the wrong premises. System-error claims are usually only confirmed once the supplier audits its own records, but the customer's job is to make the audit unavoidable.
- Lost transfer or supplier change. A change of supplier that fell into a "gap" — neither the outgoing nor the incoming supplier billed correctly — is one of the most common back-billing patterns. The contract dates and meter-read handover record demonstrate the gap.
- Fault left unaddressed. The customer reported a problem (an obviously wrong bill, a stuck meter, a smart meter showing zero) and the supplier failed to act. Written contact records — emails, web-chat transcripts, complaint reference numbers — convert this from a "he said, she said" dispute into a paper trail.
A letter template you can adapt
The text below is the skeleton we use as a starting point in our casework. Replace the bracketed elements and add the specific evidence available to you. The tone is deliberately neutral; suppliers respond to clear citation, not to indignation.
[Your name / business name] [Address] [Account number] [MPAN / MPRN as applicable] [Date] Customer Services [Supplier name] [Supplier address] Dear Sir / Madam Formal request: application of Standard Licence Condition [21BA / 7A] to back-billed charges I write in connection with the bill dated [DATE] for the supply at the above address, which seeks recovery of £[AMOUNT] for energy alleged to have been consumed between [DATE A] and [DATE B]. I do not accept the bill in its current form. The earliest portion of the charge — covering the period [DATE A] to [DATE 12 MONTHS BEFORE TRIGGER] — relates to consumption more than 12 months before the date on which an accurate bill was issued. Under Standard Licence Condition [21BA / 7A] (applying to my account as a [domestic / microbusiness] customer), [Supplier] is prevented from recovering charges for unbilled energy used more than 12 months ago where the failure to bill accurately is attributable to the supplier. In this case, the failure is attributable to the supplier because: [ONE OR MORE OF: - meter reads were submitted on [DATES] and were not actioned; - the bill rests on estimated reads despite actual reads being available in the national metering record; - the previous transfer in/out on [DATE] left the account unbilled for [PERIOD]; - a fault reported on [DATE] under reference [REF] was not addressed.] I therefore request a corrected bill capped at the 12 months immediately preceding [TRIGGER DATE], with the earlier portion written off in accordance with the licence condition. Please respond within 14 days. If the matter is not resolved within 8 weeks I will refer it to the Energy Ombudsman, whose decision is binding on the supplier. Yours faithfully [Name]
Send the letter by email and by post, and retain proof of postage. The 8-week clock for Energy Ombudsman escalation runs from the date the supplier received your complaint.
Common supplier objections (and replies)
Suppliers have a small repertoire of stock responses. The replies below are what we send when each one appears.
| Supplier objection | Reply that works |
|---|---|
| "You should have submitted reads." | The customer is not legally obliged to submit reads. SLC 21BA/7A places the obligation to bill accurately on the supplier. Estimated billing in the presence of available actuals is not accurate billing. |
| "We did send you bills." | The rule requires accurate bills, not bills per se. A quarterly estimated bill that diverges materially from actual consumption is not accurate billing for licence-condition purposes. |
| "This was a customer-side fault — the meter was inaccessible." | If the supplier has not requested access in writing, with a clear date and consequence, the inaccessible-meter defence does not stand. Provide any evidence that access was offered or attempted. |
| "As a goodwill gesture we will reduce the charge by 50%." | The licence condition caps recovery at 12 months, not at a percentage. Goodwill offers can be useful as opening positions but should not be accepted in lieu of the full protection where the rule applies. |
| "You are not a microbusiness, so SLC 7A doesn't apply." | Confirm against the SLC 7A definition: fewer than 10 employees / FTEs and turnover or balance sheet below €2m, or annual consumption below 100,000 kWh electricity / 293,000 kWh gas. Many SMEs incorrectly classed out of microbusiness status meet at least one limb. |
Escalating to the Energy Ombudsman
If the supplier fails to resolve the complaint within 8 weeks, or issues a "deadlock" letter sooner, the matter can be escalated to the Energy Ombudsman. The service is free for domestic and microbusiness customers, and the Ombudsman's decisions are binding on the supplier (but not on the customer — you can decline the decision and pursue other routes if you wish).
The Ombudsman expects to see, at minimum: a copy of the disputed bill, the original complaint letter (the template above), the supplier's response, and any correspondence in between. Decisions typically arrive within 6–10 weeks of a complete submission. Where the Ombudsman finds in the customer's favour the standard remedies are a corrected bill, removal of any debt-recovery action and, where appropriate, a goodwill payment of £50–£250 for inconvenience caused.
When the rule doesn't apply
The rule has limits. It does not apply where:
- The customer obstructed accurate billing — for example, refused access for a meter installation or repeatedly provided false reads.
- The customer is a larger business above the microbusiness threshold and is not a domestic customer. In that case common-law principles around limitation (Limitation Act 1980 — six years for contractual debts), set-off, and contractual interpretation apply instead. We routinely succeed in larger-business disputes on those grounds, but the framework is different and the documentation needs are higher.
- The supplier did bill accurately within 12 months and the customer simply failed to pay. Non-payment of an accurate bill is not back-billing.
If you are unsure whether your bill falls inside the rule, our back-billing calculator walks through the trigger date, the 12-month protected period and a quick estimate of the recoverable amount. Where the calculator suggests a meaningful claim is available we can take the casework on directly — fee-disclosed and capped where appropriate.