Shock Energy Bill for Old Usage? The 12-Month Rule (UK)
Updated 27 September 2026 · Sources listed below
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. Ofgem's back-billing rule means you do not have to pay for energy used more than 12 months ago that you were never correctly billed for — unless you acted unreasonably, for example by blocking access to the meter.
The short answer
Under Ofgem's back-billing rules, you do not have to pay for energy you used more than 12 months ago if you had not had an accurate bill for it, had not been told what you needed to pay through a statement of account, or your Direct Debit was set too low to cover it. The exception is where you acted unreasonably — for example by blocking access to your meter, ignoring requests for payment, or stealing gas or electricity. It is not an amnesty on charges you were already correctly billed for.
Contents
When the rule applies
The rule is not "anything older than a year is written off". It covers energy used more than 12 months ago that you were never correctly billed for. You do not have to prove the supplier was at fault; the supplier can only rely on the exception if you acted unreasonably.
Ofgem's rule in brief
- It applies if you had not had an accurate bill for that energy, had not been told what to pay through a statement of account, or your Direct Debit was set too low
- It does not apply if you acted unreasonably — for example blocking access to the meter, ignoring requests for payment, or stealing gas or electricity
- If you think the rules have not been followed, Ofgem says to contact your supplier right away
- It applies to energy USED more than 12 months before the bill, not to the age of the account
Evidence to gather
Records make the letter easy to check. Show which bills and statements you did and did not receive for the period, and anything that answers a suggestion that you acted unreasonably — such as readings you gave or contact you made.
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. [Say which applies: I had not received an accurate bill for this usage before / I had not been sent a statement of account showing what I needed to pay / my Direct Debit was set too low to cover it.] I have not prevented you from billing me accurately: [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 old charges you were already correctly billed for
- Not dealing with the exception, if the supplier suggests you blocked meter access or ignored payment requests
- 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 bills and statements you received, and the dates you gave any readings
- 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
Sources
- Ofgem: What to do if you get a back bill
- Ofgem: Decision introducing licence condition 21BA (back-billing)
- Energy Ombudsman: What is back billing?
- Ofgem: Complain about your energy supplier
Rules and deadlines change. Check the official source before relying on a date or amount.
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