A "catch-up" bill landing out of nowhere — sometimes for thousands of pounds, going back years — is one of the most stressful surprises an energy supplier can send. Before you assume you have to pay it in full, it's worth checking whether Ofgem's back-billing rule already protects you.
The 12-month rule, explained precisely
Under Ofgem's back-billing rules (formally Standard Licence Condition 21BA for domestic customers), a supplier cannot charge you for energy used more than 12 months ago if the reason you weren't billed correctly at the time was their fault — a broken meter-reading system, estimated bills that were never corrected, or an account that was never set up properly. The clock runs from the date of the corrected bill back 12 months, not from when the error happened.
The exception that catches some people out
This protection doesn't apply if the delay was actually your fault — specifically, if you blocked the supplier from accessing your meter, ignored repeated requests to provide a reading, or tampered with the meter. If you provided reasonable access and responded to requests for readings, the 12-month protection should apply regardless of how the supplier explains the delay.
What to check before you dispute anything
- Take a dated photo of your actual meter reading and compare it to what's on the disputed bill
- Check whether the bill says "estimated" for the disputed period — this is a strong sign the backbilling rule may apply
- Gather any record of meter readings you submitted yourself (online account, app, phone calls) that the supplier didn't act on
What to actually say
"I'm disputing the portion of this bill relating to energy used more than 12 months ago. I provided accurate meter readings and reasonable access throughout this period. Under Ofgem's back-billing rules (Standard Licence Condition 21BA), I am not liable for charges older than 12 months where the billing failure was the supplier's fault. Please issue a corrected bill removing these charges."
If they refuse
- Keep paying the undisputed portion (the last 12 months) while the dispute is ongoing — this avoids the situation escalating into a debt collection issue on top of the billing dispute.
- Raise a formal complaint in writing, citing the specific rule and the evidence above.
- If unresolved after 8 weeks, or if you receive a deadlock letter sooner, escalate to the Energy Ombudsman — this route remains at 8 weeks and hasn't changed (unlike the telecoms sector, where the wait time recently dropped to 6 weeks).
Be realistic about the outcome: alongside removing the disputed charges, the Ombudsman's typical goodwill compensation for the inconvenience is generally in the range of £50-£250 — a fair result, but not usually a large windfall beyond getting the bill itself corrected.
See also: how to escalate to the Energy Ombudsman, and free Citizens Advice help with energy bills and switching.