Reference guide — UK energy supply licence
SLC 21B vs SLC 21BA: the difference suppliers miss
Two licence conditions, two different obligations, one common mistake: treating a long run of estimated bills as proven back-billing exposure. This guide separates the two, shows the evidence each requires, and explains why the distinction decides whether your risk figures survive scrutiny.
Side by side
| Aspect | SLC 21B | SLC 21BA |
|---|---|---|
| What it governs | Billing accuracy — bills must reflect actual readings where held or reasonably obtainable. | Back-billing — a 12-month limit on charging for previously unbilled consumption. |
| Trigger | An estimated bill issued after a valid actual read, or no actual read in 12 months. | A catch-up bill that reaches behind the 12-month window. |
| Evidence needed | Reading history: dates, actual/estimated indicators, consumption per bill line. | Bill date, consumption period, validated vs billed consumption, tariff, standing charge, VAT. |
| What a flag means | A review candidate. Not a breach, not a £ figure. | Potential unrecoverable amount — only after the evidence above exists. |
| Carve-outs | Context matters: failed reading attempts and appointment history are not visible in the data. | Customer obstruction or theft of energy must be evidenced, not asserted. |
Why the conflation happens
The two conditions meet at the same account. A customer billed on estimates for eighteen months is exactly where a catch-up bill is eventually issued — and exactly where the 12-month back-billing limit bites. Because the same population triggers both rules, it is tempting to treat one flag as proof of the other. It is not. SLC 21B tells you where to look; SLC 21BA tells you what, if anything, is financially exposed. Between the two sits evidence: bill dates, consumption periods and a validated-versus-billed comparison that most billing extracts do not carry by default.
The full screening rule set — including how the aged under-billed difference is priced, and when "not quantified" is the only honest answer — is published on the methodology page. For the conditions themselves, Ofgem's supply licence conditions are the authoritative source.
The five questions suppliers actually ask
- What is the difference between SLC 21B and SLC 21BA?
- SLC 21B concerns billing accuracy: a supplier must base a customer's bill on an actual meter reading where it holds one or can reasonably obtain one. SLC 21BA is the back-billing rule: it prevents a supplier from charging a domestic or micro-business customer for energy used more than 12 months before the accurate bill was issued. The first is about how you bill; the second is about how far back you can charge.
- Does 365 days without an actual reading prove an SLC 21BA breach?
- No. A long run of estimates is an SLC 21B review flag — a reason to look at the account. SLC 21BA exposure requires separate evidence: the bill date, the consumption period covered, and proof that validated actual consumption exceeds what was billed, with part of that consumption older than 12 months at the bill date.
- Why does conflating the two conditions matter?
- Because it corrupts your risk figures in both directions. Treating every long-estimate account as back-billing exposure inflates the £ at risk with amounts you may never have under-billed. Treating a genuine 21BA issue as a mere 21B flag understates real exposure. An audit that cannot separate the two cannot defend either number.
- What evidence is needed to assess SLC 21BA properly?
- Per account: the bill date, the start and end of the consumption period, the validated actual consumption, the cumulative consumption already billed, the tariff, applicable standing-charge days, and the VAT treatment. Only the positive validated-versus-billed difference attributable to consumption older than 12 months is priced — and even then it is an indicative screening estimate, not a determination.
- What if the data needed for SLC 21BA is missing?
- The account stays an SLC 21B review flag and the exposure is shown as 'not quantified'. Inventing a £ figure from incomplete data is worse than no figure — it will not survive challenge by an auditor, the Energy Ombudsman, or your own board.
Important
This page is a plain-language reference, not legal advice, and it is not a determination that any licence breach has occurred. The licence conditions themselves, and Ofgem guidance, are the authoritative source. PowerView output is a triage signal for your own review; every £ figure is an indicative screening estimate, never a determined exposure.
Screen your own portfolio in 48 hours
PowerView separates the two conditions by design: SLC 21B flags stay unmonetised review candidates, and SLC 21BA is assessed only where bill date, consumption period and validated-versus-billed evidence exist — priced as an indicative screening estimate with standing charge and VAT applied. Every figure is written to an immutable SHA-256 audit trail you can re-verify.