Energy Back-Billing: The 12-Month Rule and How to Challenge a Catch-Up Bill

You open your post to a shock energy bill for hundreds or thousands of pounds — usage your supplier "forgot" to charge you for, sometimes going back years. This is called back-billing, and strict rules limit what you can be made to pay.

The 12-month back-billing rule

Under Ofgem's rules, an energy supplier cannot charge you for gas or electricity you used more than 12 months ago if it failed to bill you correctly for it and the under-charge was not your fault. This protection applies to domestic customers and most small businesses.

In plain terms: if the supplier's own error (a missed bill, an estimated reading they never corrected, a faulty meter they did not act on) caused the catch-up bill, anything older than 12 months should be written off.

When the rule does not protect you

• You prevented accurate billing — for example, you repeatedly refused meter readings or access.
• You were told about the under-charge and chose to ignore it.
• You knowingly used unregistered or tampered supply.

If none of these apply, the 12-month cap should stand.

How to challenge a back-bill

1. Do not pay the disputed amount in full while it is in dispute — but do keep paying for current, correctly billed usage.
2. Ask the supplier in writing to apply the back-billing rule and remove charges for usage over 12 months old.
3. Request a clear breakdown of the bill, meter readings, and why it was not billed at the time.
4. Agree an affordable payment plan for any genuinely owed amount within the 12-month window.
5. Escalate to the Energy Ombudsman (free) if the supplier refuses after eight weeks or issues a deadlock letter.

A letter to send

Dear [Supplier],

Re: Account [number] — back-billing challenge

On [date] I received a catch-up bill of £[amount] covering usage from [period].
Under Ofgem's back-billing rules you cannot charge for energy used more than 12
months ago where correct billing did not happen through no fault of mine. I did
not prevent accurate billing.

Please remove all charges relating to usage more than 12 months before the date
of this bill, send me a corrected statement, and confirm an affordable plan for
any remaining balance. If I do not receive a satisfactory response within eight
weeks, I will refer this to the Energy Ombudsman.

Yours faithfully,
[Your name and account details]

Back-billing rules exist precisely because suppliers' mistakes should not become your emergency. Quote the 12-month limit clearly and most catch-up bills shrink dramatically — or disappear.