What counts as 'unreasonable behaviour' under the back-billing rules?

Great Britain · Rules checked 24 October 2026 · Not legal advice

Free tool: Back-billing calculator. Enter the bill date and the period charged to find the 12-month line.

The 12-month rule doesn't apply if the supplier couldn't bill you correctly "due to obstructive or manifestly unreasonable behaviour" by you (SLC 21BA.2(c)). Suppliers sometimes use this to refuse back-billing complaints, so it's worth knowing where the line is.

Examples Ofgem gives

Ofgem's back-billing page lists:

• stopping your supplier from billing you accurately, including by blocking access to your meter;
• ignoring requests for payment from your supplier;
• stealing electricity or gas.

What isn't enough on its own

Ofgem's 2020 open letter says a customer's failure to provide a meter reading will not absolve the supplier from the limit, and that suppliers should keep evidence of the contacts they attempted and the methods they used. It also says customers must not be held responsible for failing to spot billing errors.

MoneySavingExpert reports that Martin Lewis has told MPs the "obstruction" test is poorly defined, so there are grey areas. If your supplier relies on it, ask it to say exactly what you did and send its evidence: dates of reading requests, access attempts and letters.

Build your evidence

• Any readings you gave (emails, app screenshots, photos).
• Times you contacted the supplier asking for a bill.
• Proof you were at the address, or reasons you couldn't provide access.