Most UK energy customers have never heard of Standard Licence Condition 21BA, but it’s one of your most powerful protections. In simple terms: if your supplier fails to bill you accurately, they cannot charge you for energy used more than 12 months ago—unless you prevented them from billing you. Despite this, suppliers and even the Ombudsman often claim it doesn’t apply. Click the links below to read Ofgem’s actual regulations:
ELECTRICITY ACT 1989: Standard Conditions of Electricity Supply Licence Condition 21BA. Backbilling 21BA.1 Subject to paragraph 21BA.2, where the licensee or any Representative issues a Bill or sends a statement of account in respect of Charges for the Supply of electricity to a Domestic Customer, or where the licensee otherwise takes steps to recover Charges for the Supply of electricity from that Domestic Customer (“a charge recovery action”), the licensee may only recover Charges for the period of 12 months preceding the date on which the charge recovery action was taken. 21BA.2 Paragraph 21BA.1 (and any paragraph of this condition which refers to it) does not apply in relation to charges for the Supply of electricity to a Domestic Customer where: (a) the charge recovery action was taken prior to the date this condition took effect; or (b) the licensee or any Representative has taken a charge recovery action following the earlier under-charging of the Domestic Customer in a manner which complied with paragraph 21BA.1 and, due to non-payment, are continuing to take steps to obtain payment for the same units of electricity and, where applicable, the same amounts in respect of a Standing Charge or other type of supply charge; or (c) the licensee has been unable to take a charge recovery action for the correct amount of electricity consumed due to obstructive or manifestly unreasonable behaviour of the Domestic Customer; or (d) any other circumstances, which following consultation, the Authority may specify by publishing a statement in writing. 21BA.3 The licensee must ensure that the terms and conditions of each Relevant Contract comply with the provisions of this condition. 21BA.4 The licensee must ensure that each Relevant Contract contains terms and conditions which reflect the effect of the provisions of this condition. 21BA.5 The licensee must not enforce or take advantage of any term of a Relevant Contract if: (a) the inclusion of that term is incompatible with this condition; or (b) the enforcement or taking advantage of that term would be so incompatible. Definitions (Part A) 21BA.6 “Relevant Contract” means any Domestic Supply Contract and Deemed Contract.
GAS ACT 1986: Standard Conditions of Gas Supply Licence Condition 21BA. Back-billing Part A: application to Domestic Customers 21BA.1 Subject to paragraph 21BA.2, where the licensee or any Representative issues a Bill to a Domestic Customer or otherwise seeks to recover (including via a Prepayment Meter) Charges for the Supply of Gas from that Customer (hereafter a “charge recovery action”), the licensee must only do so in respect of: (a) Units of Gas which could reasonably be considered to have been consumed within the 12 months preceding the date on which the charge recovery action was taken; and (b) where applicable, amounts in respect of a Standing Charge or any other type of supply charge accrued within the 12 months preceding the date on which the charge recovery action was taken. 21BA.2 Paragraph 21BA.1 does not apply in relation to charges for the Supply of Gas to a Domestic Customer where — (a) the charge recovery action was taken prior to the date this condition took effect; or (b) the licensee or any Representative has taken a charge recovery action following the earlier under-charging of the Customer; or (c) the licensee has been unable to take steps to recover the Charges that it would otherwise have been entitled to recover because the Customer has engaged in obstructive or manifestly unreasonable behaviour.
When You’re Protected
SLC 21BA applies when:
- Your supplier sends you a catch-up bill for past usage
- The charges cover energy used more than 12 months ago
- You never received an accurate bill for that period, despite behaving reasonably
How it works: Identify your first accurate bill date. Count back 12 months. All charges before that (usage, standing charges, VAT) must be written off.
The Only Exceptions
Protection doesn’t apply only if:
- The bill predates when the rules came into force
- Previous charges already complied with the 12-month rule
- You prevented accurate billing through obstructive behaviour (denying meter access, tampering, refusing to engage)
- Ofgem gave specific written direction for an exception
If none of these apply, SLC 21BA protects you.
Common Supplier Tactics (And Why They’re Wrong)
“You had estimated bills, so we can back-bill everything.”
Wrong. Estimates aren’t accurate bills. If they turned out incorrect, you haven’t been properly billed. Protection still applies.
“You gave us readings, so protection doesn’t apply.”
Wrong. The question is whether the supplier billed you accurately in good time. If their systems failed despite you providing readings, protection applies.
“Your account was in credit, so SLC 21BA doesn’t count.”
Wrong. The licence doesn’t make this distinction. Protection is about charging for past supply, not account balance.
“We rebilled internally, so the 12-month clock starts then.”
Wrong. What matters is when you received an accurate bill, not internal system adjustments.
Where the Ombudsman Goes Wrong
The Ombudsman does not always interpret SLC 21BA correctly. In some cases, they may rely too heavily on a supplier’s explanation or overlook important details about how the rule is meant to work.
That’s why it’s important to know your rights and point directly to the official Ofgem rules and guidance. When you clearly reference the licence condition itself, you ensure the decision is based on the actual regulations—not assumptions or supplier interpretations.
How to Use Your Rights
- Identify when you received your first accurate bill
- Count back 12 months from that date
- Demand write-off of all charges before that window
- Quote SLC 21BA explicitly
- Challenge any made-up caveats by asking for the specific licence clause
Final Word
SLC 21BA is a binding licence condition, not a favour. If you’re being billed for over a year of historical usage due to supplier mistakes, you’re entitled to challenge it. Unless they can point to a specific exception in the licence, insist the 12-month limit is observed.