# Energy back-billing and the 12-month rule: how to challenge a catch-up bill
The bill lands with a new line on it — “catch-up charge” — and a figure that reaches back across last year and the year before, months you were sure were paid and closed. Before the panic sets in, hold onto the one fact that matters: under Ofgem’s back-billing rule, a supplier cannot recover charges for gas or electricity you used more than twelve months ago if it failed to bill you accurately at the time and the shortfall was not your fault. That rule is Standard Licence Condition 21BA, written into every domestic supply licence since May 2018. It covers both fuels. It has done for years.
Here is what typically happens. The meter goes unread for a long stretch — nobody visits, the estimates roll over, and the monthly figure looks steady because it is invented. Then something triggers a real reading: a switch, a new smart meter, an engineer at last. The account is reviewed. And a single letter arrives asking for a year, or two, of the difference between what was guessed and what was actually used. It is a large number, and it is presented as though it were simply arithmetic — as though the missing months had never been anyone’s job.
They were. The rule does not care that the energy was genuinely used, or that the sum is technically sitting on a meter somewhere. It anchors on the date you were last correctly billed, not the date someone finally read the dial. Energy burned twenty months ago and billed for the first time today falls on the wrong side of the twelve-month line. The exceptions are narrow and specific: you obstructed access to the meter, you tampered with it, or you took energy without paying. Outside of those, the older portion of a catch-up bill is not something you are required to pay — however confidently the letter asks.
So the argument is rarely about whether the money was owed in some abstract sense. It is about a date. What was the last accurate bill, and how far behind it does this new demand reach? Dig out the old statements. Find the readings marked with the little “E” for estimated, and the point where a genuine reading finally appears. The gap between those two is the territory the rule protects.
None of this needs a solicitor, and it should not cost you a penny. The free route comes first. The Citizens Advice consumer service will talk it through at no charge and knows this rule well. You raise a formal complaint with the supplier, in writing, quoting the back-billing rule and setting out the dates. If eight weeks pass without resolution, or the supplier sends a “deadlock” letter sooner, the matter can go to the Energy Ombudsman. That service is free to you; it is funded by the suppliers themselves. Its decision binds the supplier — which has 28 days to act on it — but not you: reject it, and every other option stays open. You have twelve months from the deadlock letter to refer.
What most people struggle with is not the principle. It is the letter — laying out the dates plainly, naming the right rule, and asking for the pre-twelve-month charges to be removed without either grovelling or squaring up to a call-centre. This is where Chris comes in. You describe what arrived and when the meter was last actually read; Chris walks you through it, keeps the tone level, and assembles the complaint around Standard Licence Condition 21BA and your own billing dates. eLitigant keeps guidance like this in the open, free to read, because the whole point is that you can do this yourself.
And at the end, here it is: a complete written complaint, dated, addressed to your supplier, citing the back-billing rule and setting out exactly which charges fall outside the twelve months — with the free Energy Ombudsman referral ready to follow if eight weeks pass or the deadlock letter lands. Not a threat. A record. The thing a fair reviewer needs in front of them to put the number right.
Draft my document with Chris →
Most people arrive for one letter and come back for the next.