A catch-up energy bill can contain charges you do not owe. Before accepting the balance, check whether your supplier is newly charging for energy used more than 12 months earlier, or chasing an accurate bill it already sent. That distinction can change what you have to pay.
This guide covers domestic gas and electricity supplied by licensed suppliers in Great Britain: England, Scotland and Wales. Northern Ireland, communal heat networks and energy resold by a landlord need their own rules checked. This is general consumer information, not advice on an individual legal dispute.
What the 12-month rule protects
Ofgem says you do not have to pay for energy used more than 12 months ago where you had not previously received an accurate bill or statement telling you what was owed, or your Direct Debit had been set too low. Exceptions apply where you have acted unreasonably. Start with its back-billing guidance when checking your bill.
Keep three things separate on paper: the dates of consumption, the dates of the bills and the payments you made. A large balance on the screen does not explain how it got there. Neither does the word “adjustment”. Ask whether the supplier is correcting readings, collecting an existing debt or adding energy it never charged for.
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Find the cutoff, then split the bill
The licence rule looks back 12 months from the relevant charge recovery action. It covers standing charges as well as units of energy. An earlier compliant demand for the same charges matters: a later reminder does not restart protection. See the annotated condition in Ofgem's supplier guidance, pages 3–4.
This licence condition took effect on 1 May 2018 and does not apply retrospectively to recovery action before then. If your dispute includes such an old demand, ask Citizens Advice or energyadvice.scot to check the position. See the pre-commencement exception in Ofgem's annotated condition 21BA.2(a), pages 3–4.
Hypothetical example: suppose the supplier first correctly seeks these previously unbilled charges on 5 November 2026. The reference date is 5 November 2025. Assume you have not obstructed accurate billing and no earlier compliant demand covers these charges. This table illustrates the date check, not a decision on a real account.
| Consumption period | Question to ask |
|---|---|
| 1 July–4 November 2025 | Older than the reference date. Ask the supplier to remove protected newly billed charges. |
| 5 November 2025–4 November 2026 | Within the 12-month window. Check readings, rates and payments before accepting the amount. |
| A charge already correctly billed in time | Check the earlier bill. Its age now does not itself cancel an unpaid balance. |
Do not divide the total by the number of months and write off a fraction. That would assume usage and charges were identical throughout. Instead, ask for the supplier's allocation across the cutoff, including the readings or estimates used. If one billing period straddles that date, mark that row for explanation rather than guessing a split.
For your own worksheet, add columns for “previously charged”, “payments credited” and “supplier's proposed correction”. Put a question mark where a figure is missing. You want a calculation you can follow. A single meter reading cannot reconstruct years of consumption for you.
Supplier mistakes and customer obstruction are different
Missing a request to submit a meter reading does not automatically remove protection. Ofgem's supplier guidance, pages 2 and 4, distinguishes that from obstructive or manifestly unreasonable behaviour. It also says customers should not be held responsible for spotting billing errors or an accumulating debt.
Blocking meter access, ignoring payment requests and stealing energy are examples in Ofgem's consumer guidance. If the supplier relies on an exception, ask which conduct prevented correct billing and request the dates and records. An unexplained “you should have noticed” is not a useful account of what happened.
Write down your side just as carefully. Were readings sent through an app? Did an appointment take place? Was a faulty meter reported? Keep the acknowledgement as well as your original message. Explain any gaps honestly; do not rewrite events to fit the rule.
Get the paperwork together
I would start with just two documents: the disputed bill and the statement immediately before it. Save copies outside the supplier's online account so you can compare them if the account changes. Use the bill-reading guide to identify the account, meter and charging periods.
- Mark the invoice date, consumption dates and every reversed or replacement charge.
- List actual and estimated readings, their dates and the meter serial number. A current photograph records today's position; it cannot prove last year's usage.
- Match payments to the account ledger. Flag missing credits separately from disputed charges.
- Collect submitted readings, fault reports, appointment records and previous complaints.
- Write the outcome you want: a dated calculation, removal of protected charges, corrected statements and any refund due.
If the meter display is confusing, use the meter-reading instructions before sending a new reading. Keep the paperwork in date order and leave out unrelated attachments. Make it easy for the complaints handler to see what went wrong.
Ask for a written back-billing assessment
Send the complaint through the supplier's published complaints route. Here is an original wording example to adapt with your own facts:
Please review bill [reference], dated [date], under the 12-month back-billing rules. It includes consumption from [period] that appears not to have been correctly charged before. Please identify the relevant recovery date, any earlier accurate bills you rely on, the protected amount and the calculation of the remaining balance. If you consider an exception applies, please explain the evidence. Please confirm my complaint reference and how disputed collection activity will be handled during the review.
Do not assume collection activity has stopped because you asked for a pause. Get the response in writing. Keep valid current charges separate, and discuss affordability promptly if you cannot pay them. Cancelling a Direct Debit by itself does not resolve the dispute; checking the payment calculation is a separate task.
If the supplier does not put it right
Keep the date you first complained. You can take an unresolved complaint to the Energy Ombudsman after eight weeks, or sooner with a deadlock letter. Ofgem regulates suppliers but does not decide individual disputes. Its complaints guide sets out the process and points to Citizens Advice in England and Wales, and energyadvice.scot in Scotland.
Before accepting a correction, compare the new statement with your worksheet. Are the protected rows removed? Are all payments still credited? Does the opening balance match the explanation? Keep both versions. Once this bill is settled, regular readings and saved confirmations give you a clearer record for the next one.