There is a small letter printed next to the number on an energy bill, and almost nobody looks at it. An A means somebody went to the meter. A C means you sent the figure in yourself. An E means nobody read anything, and the amount you are being asked to pay was produced by a model of a household that resembles yours.
Most months this is harmless. The estimate runs a little high or a little low, the next real reading corrects it, and the account settles. The letter only matters when the correction does not arrive for two years, and then it arrives all at once.
The letter beside the number
Trust in a bill does not come from the brand on the envelope. It comes from a chain that any ordinary person could, in principle, walk backwards: a physical dial in a cupboard, a number written down, an arithmetic step, a total. Each link is dull, and the dullness is the point. You do not have to believe anybody. You can go and look.
An estimate quietly removes the first link and leaves the rest standing. The bill still has the shape of a measurement. It has decimal places, a period covered, a tariff rate, a running balance. What it does not have is the thing all of that is supposed to be about, and there is no visual difference between the two documents except one letter that nobody was ever taught to read.
What an estimate is actually made of
Estimates are not guesses. They are built from your own past consumption where it exists, adjusted for the season and for how cold it has been, and from a profile of what similar properties use where it does not. For a household whose life has not changed, this is usually close.
The failures cluster exactly where you would expect. Somebody moves in and the profile still describes the family who left. A room becomes an office and the heating pattern changes. A tenant inherits the previous occupant's opening reading because nobody wrote one down on the day of the handover. In every case the model keeps producing confident numbers while drifting further from the dials, and nothing in the process raises a hand.
That is the part people find hardest to forgive afterwards. The system was not silent about the problem. It was fluent about it, month after month, in a tone indistinguishable from certainty.
Three million meters that stopped talking
The obvious fix was to take the reading out of human hands, and Britain has spent more than a decade doing exactly that. The government's quarterly statistics for June 2026 put 39 million smart meters in domestic properties operated by large suppliers, against 15 million that are still not smart. Three quarters of properties now have a smart electricity meter.
Then comes the number that keeps the letter E in business. About 3.08 million of those smart meters were running in what the statisticians call traditional mode, which means the hardware is on the wall and the communication is not working. By fuel, 3.8 percent of properties have a smart electricity meter in that state, and 6.4 percent a smart gas meter.
| Great Britain, end June 2026 | Share of properties |
|---|---|
| Smart electricity meter, in smart mode | 71% |
| Smart electricity meter, traditional mode | 3.8% |
| Smart gas meter, in smart mode | 50% |
| Smart gas meter, traditional mode | 6.4% |
A meter in that condition is the worst of both arrangements. The householder believes the reading is automatic and stops sending figures in. The supplier has no data and falls back to the model. Nobody is lying to anybody, and the gap between the account and the cupboard widens by a few pounds a month for as long as it lasts.
A twelve month wall, and who built it
Regulators eventually stopped treating the catch-up bill as an accounting matter and started treating it as a question about who should carry the risk of an unverified number. On 5 March 2018 the British energy regulator announced that it would ban suppliers from backbilling customers beyond 12 months. The rule took effect for households that May and for small businesses the following November.
The figures behind the decision explain the shape of it. The median domestic catch-up bill in 2016 and 2017 was 1,160 pounds, covering a median of 24 months, and the regulator noted extreme cases running past 10,000 pounds. The exception is narrow and sensible: a customer who tampered with the meter or blocked access to it cannot then use the time limit as a shield.
What the rule does is simple. If the supplier could have measured and did not, the cost of that omission stops at a year and stays with the supplier. It converts an open-ended liability sitting on the household into a bounded one sitting on the party that had the power to prevent it.
Why the catch-up bill lands as betrayal
People absorb large bills they expected. What they do not absorb is a large bill for a period they already believed was settled, because that demand contains a second claim underneath the first: everything you were told during those months was provisional, and you were not informed of that.
A household that has paid every demand on time has done the only thing the relationship asked of it. Being told afterwards that compliance bought nothing is the specific injury, and it is why these disputes run hotter than the amounts alone would suggest. The same mechanism runs through anything that promises a settled state and then reopens it, and the damage lands on the next interaction rather than this one.
One reading, written down, before winter
The defence is unglamorous and takes about four minutes twice a year.
- Pull out the most recent bill and find the code beside each reading. If it says the reading was estimated, you have been paying against a model, and it is useful to know for how many periods in a row.
- Go and read the dials yourself, photograph them with the date visible, and send the figures in. A photograph converts your account of the number into evidence of it.
- If you have a smart meter, check that the supplier is actually receiving from it rather than assuming so. Gas units in particular drop off, and the household is usually the last to know.
- On any move, take a reading at the door on the day, with a photograph, and keep it. Most inherited debt disputes trace back to a number nobody wrote down at a handover.
- If a large catch-up demand arrives, ask in writing which periods it covers and on what basis, and check the answer against the 12 month rule before agreeing a payment plan.
None of this makes the bill smaller. It restores the one property that makes a charge acceptable, which is that somebody outside the billing system can go and check it. A number you can walk to and check is a different object from one you have to accept, even when the two are identical, and institutions that forget the difference spend years rebuilding what a single unread dial cost them.