A bill arrives out of nowhere for gas or electricity used over a year ago, sometimes running to four figures. If the delay was your supplier's fault, Ofgem's back-billing rule may mean you don't have to pay it.
What the back-billing rule actually says
Ofgem bans domestic energy suppliers from issuing a "catch-up" bill for gas or electricity used more than 12 months ago, where the reason the customer wasn't billed correctly at the time was the supplier's fault. These bills, often the result of estimated readings, ignored smart meter data, or an internal billing error, have historically averaged over £1,000 when they land.
The rule isn't a courtesy policy — Ofgem confirmed it as a formal ban on backbilling beyond 12 months for domestic and microbusiness customers, closing a gap in the earlier voluntary agreement that some suppliers weren't following consistently.
When the 12-month limit protects you
- Your supplier never sent an accurate bill for that period, despite you requesting one
- You were billed using estimated readings instead of actual readings you or a meter reader provided
- Your supplier mixed up meter readings or account details and failed to correct it when you flagged it
- Your supplier ignored a query or fault you raised about your account and let a large balance build up silently
When it doesn't apply
The protection has a specific carve-out: if you actively prevented the supplier from taking or receiving accurate readings — for example by repeatedly blocking meter access — the 12-month limit may not protect you, and the supplier can potentially recover charges going back further.
It's also worth separating back-billing from simple non-payment. If you were billed correctly and on time but didn't pay, that's a debt, not a back-bill, and the 12-month rule doesn't erase it.
How to challenge an overdue back-bill
- Check whether the disputed usage falls entirely outside the 12-month window from when the error was discovered and the corrected bill issued.
- Gather your bill history, any meter readings you submitted, and any prior contact where you flagged a suspiciously low or missing bill.
- Write to the supplier stating that under Ofgem's back-billing rule, they cannot charge for energy used more than 12 months ago where the error was theirs, and request a revised bill.
- Ask for a reasonable payment plan for any portion that is legitimately owed — suppliers should generally offer a repayment period matching the length of time the debt built up.
- If the supplier refuses, escalate: raise a formal complaint, wait the required period, then refer to the Energy Ombudsman if unresolved.
What this means practically
- A shock catch-up bill over 12 months old isn't automatically valid — check who was at fault first.
- Estimated billing and ignored smart meter data are common triggers for a valid back-billing challenge.
- You remain responsible for any usage within the last 12 months, even if the total bill spans longer.
- Keep every bill and meter submission — the evidence needed to challenge a back-bill is exactly what a routine bill audit already collects.
Sources
- Ofgem — Ban on backbilling beyond 12 months: ofgem.gov.uk
- Citizens Advice / MoneySavingExpert — Back-billing rules and exceptions: moneysavingexpert.com
Related Kibbo Tools
- Utility Bill Audit Checklist — spot estimated readings and billing errors before they turn into a large back-bill.
- Utility Meter Reading Checklist — submit accurate readings correctly so suppliers can't claim they never had real data.