Shock Energy Bill for Old Usage? The 12-Month Rule (UK)
A sudden bill for energy used a year or more ago is one of the few situations where the rule is squarely on your side — but it turns on whose fault the under-billing was, and that is the part most people never argue.
The short answer
Under Ofgem's back-billing rules — Standard Licence Condition 21BA for domestic customers — a licensed gas or electricity supplier cannot recover charges for energy used more than 12 months ago where the supplier was at fault for not billing accurately in that time and you acted reasonably throughout. It is not an automatic amnesty on old debt: both halves of that test matter.
Contents
The two halves of the test
The rule is not "anything older than a year is written off". It applies where the supplier was at fault for the failure to bill, and where you behaved reasonably. Both need to be argued, and the second is the one people forget to evidence.
What has to be true
- Supplier at fault: estimated bills despite readings being given, readings ignored, no bill issued at all, or a known billing failure
- You acted reasonably: readings submitted, the problem reported, contact not ignored
- Where you blocked access to the meter or never engaged, the rule is much weaker
- It applies to energy USED more than 12 months before the bill, not to the age of the account
Evidence that decides it
This is a documentary argument, and it is usually won or lost on whether you can show readings went in and were not used. Gather that before writing, because "they never billed me properly" without dates is easy to refuse.
What to gather first
- Dates you submitted meter readings, and how
- Any bill marked estimated where you had given a reading
- Any period with no bill at all
- Records of contact — calls logged, emails, chat transcripts
If they refuse
This is a complaint like any other, so the escalation route is the supplier's complaints process and then the Energy Ombudsman. Do not pay a disputed back-bill simply to stop the pressure without saying in writing that it is paid under protest and the dispute continues.
Back-billing challenge
Edit this template with your facts, dates, and requested outcome before sending.
Subject: Back-billing challenge — account [number] Dear [Supplier], On [date] I received a bill for [amount] covering usage from [start date] to [end date], account [number]. A substantial part of this covers energy used more than 12 months before the bill was issued. [Set out briefly why the supplier was at fault — for example that meter readings were submitted and not used, that estimated bills were issued despite actual readings being provided, or that the account was not billed at all for a period.] I have acted reasonably throughout: [for example, readings submitted on these dates, or the issue reported on this date]. Under Ofgem's back-billing rules I ask you to remove charges for energy used more than 12 months before the date of the bill, and to send a corrected bill. Please confirm in writing within 14 days. Kind regards, [Your Name]
Common mistakes to avoid
- Assuming the rule cancels any old debt regardless of whose fault it was
- Not evidencing your own reasonable conduct, which is half the test
- Arguing about the total rather than identifying the portion older than 12 months
- Paying in full to stop the letters, then trying to reclaim it afterwards
- Not asking for a corrected bill, so the account stays wrong even if charges are dropped
- Missing that the test is when the energy was USED, not when the account opened
Next steps
- 1Work out which part of the bill covers usage more than 12 months old
- 2Gather the dates you gave readings and any estimated bills
- 3Write to the supplier citing the back-billing rules and asking for a corrected bill
- 4If you pay anything meanwhile, say in writing that it is under protest
- 5If refused, use the complaints process and then the Energy Ombudsman
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