Ofgem back billing rules explained without the supplier jargon
Use this page when the supplier mentions back billing rules, old charges or a catch-up balance and you need to know what to ask for next.
Best next steps
What to ask the supplier to identify
The period
Which dates are included in the old charge?
The readings
Were they actual, estimated, smart or customer readings?
The reason
Why was the amount not billed correctly earlier?
The rule position
Does the supplier say the back billing rules do or do not apply?
Supplier wording
Please explain how the back billing rules have been applied to this bill. Identify any charges relating to energy used more than 12 months before the bill date and explain whether those charges should be removed or corrected.
Back billing cluster
The rule itself, in one paragraph
Standard Licence Condition 21BA is the back-billing rule for domestic customers. It says a supplier must not charge you for gas or electricity used more than 12 months before the date of the bill, where the supplier is the reason you were not billed accurately during that period. It has applied to every licensed supplier in Great Britain since 1 May 2018. Microbusinesses get the same protection under SLC 7A.
Two things in that sentence do most of the work, and most complaints are lost on them:
- “12 months before the date of the bill.” The clock runs backwards from the bill, not from when you noticed, not from when the meter was last read, and not from when you first complained. A bill dated 3 September 2026 cannot properly charge you for energy used before 3 September 2025 if the supplier was at fault.
- “Where the supplier is the reason.” The protection is about supplier failure. If the supplier can show you obstructed accurate billing — refused meter access, ignored repeated reading requests, or behaved in a way the rule calls manifestly unreasonable — the protection can fall away for that period.
Source: Ofgem, Modification of the electricity and gas supply licences to introduce rules on backbilling, in force 1 May 2018. Always check the current licence text before quoting a condition number to a supplier — conditions are amended.
When the protection does not apply
Suppliers do sometimes have a real answer. It is worth knowing which ones are legitimate, because arguing against a valid exception wastes the eight weeks you need before you can escalate.
| What the supplier says | Does it hold up? | What to ask for |
|---|---|---|
| “You blocked access to the meter.” | Potentially valid. This is the main exception in the rule. | Dates of every access attempt, the letters or texts sent, and what response was recorded. |
| “You never gave us readings.” | Only if they asked and you did not respond. Silence from the supplier is their failure, not yours. | The reading-request history, and your own submitted readings from the app or account. |
| “This is a catch-up bill, not a back bill.” | Often true and often the real answer. | A period-by-period breakdown, so you can see which side of the 12-month line each charge sits on. |
| “The rule does not apply because you changed supplier.” | Weak. The obligation follows the supplier that failed to bill. | Which licensed entity billed each period, and the final statement from the losing supplier. |
| “There was a meter fault, so we could not bill.” | A fault is normally the supplier's problem to detect and fix. | When the fault was first flagged in their system and what they did about it. |
| “It was a billing system migration.” | Not an exception. An internal IT project is supplier fault. | Written confirmation that the delay was caused by their systems. |
Notice the pattern: almost every valid exception depends on something the supplier must be able to evidence. Asking for that evidence, in writing, is the whole move. A supplier that cannot produce a record of asking you for readings has effectively conceded the point.
What Ofgem will and will not do for you
This is the part people get wrong most often, and it costs them weeks. Ofgem does not handle individual complaints. It writes and enforces the licence conditions that suppliers operate under, and it takes enforcement action against suppliers at company level. It will not open a case about your bill.
| Body | What it actually does | Use it when |
|---|---|---|
| Your supplier | Must operate a complaints process and issue a final response. | Always first. Nothing else opens until you have done this. |
| Energy Ombudsman | Free, independent, decides individual disputes. Binding on the supplier. | After 8 weeks, or immediately on a deadlock letter. |
| Citizens Advice consumer service | Free advice, and can refer vulnerable cases to the Extra Help Unit. | When you want help preparing, or you are at risk of disconnection. |
| Ofgem | Sets and enforces the rules across the market. | Never for a single bill. Worth reading for the rule text itself. |
So quoting the rule to your supplier is useful. Threatening to “report them to Ofgem” is not, and experienced complaint handlers know it. Say you will refer the matter to the Energy Ombudsman on a specific date instead. That one is real.
The letter, written out in full
Copy, fill in the square brackets, send by email
Numbering the requests matters more than the tone. A numbered list is harder to answer with a paragraph of general reassurance, and if it goes to the Ombudsman, it shows exactly which questions the supplier declined to answer.
Frequently asked questions
Is this page official Ofgem advice?
No. It is a plain English support page that helps you understand what to ask the supplier and where to check official sources.
What is the main mistake people make?
They argue about the total amount without identifying the period, readings and older charges.
Is this page official Ofgem guidance?
No. It is a plain-English explanation of what the licence condition says and what to do with it. The licence text itself is published by Ofgem and is the authority; this page is not affiliated with Ofgem.
Can I complain to Ofgem directly about my bill?
No. Ofgem regulates suppliers but does not adjudicate individual disputes. Your route is supplier complaint, then Energy Ombudsman.
Does the rule apply to prepayment meters?
The back-billing protection applies to domestic supply generally. Prepayment cases usually surface as a debt loaded onto the meter rather than a paper bill, so ask for the date and period of every debt amount applied to the meter.