The back billing rule is an Ofgem protection that stops energy suppliers charging customers for gas or electricity used more than 12 months ago, where the customer was not correctly billed for it through the supplier's fault. It limits how far back unbilled charges can reach.
In one line: The back billing rule bars suppliers from recovering energy charges older than 12 months that went unbilled through the supplier's own fault.
How the back billing rule works
The rule applies where the supplier failed to bill accurately despite having the information needed, for example after missed readings or its own errors. It does not erase debt the customer was already correctly billed for and left unpaid.
If a supplier suddenly issues a catch-up bill covering 18 months of unbilled usage worth 900 GBP, the portion relating to energy used more than 12 months before the bill, say 300 GBP, cannot be charged under the rule.
The protection is set out in supplier licence conditions enforced by Ofgem and applies to domestic and microbusiness customers.
Back billing vs estimated billing
Estimated billing is about how a current bill is calculated when no reading exists, whereas the back billing rule limits how far into the past a supplier can reach to recover charges it should have billed earlier.
The rule only bites where the supplier was at fault, so it does not apply if the customer obstructed access or prevented accurate billing.
Primary source: Ofgem: Back billing for households