Working checklist — estimated billing controls
Auditing estimated billing under SLC 21B: the checklist
A practical, seven-step checklist for compliance and revenue-assurance teams at UK energy suppliers: the data to extract, the patterns to flag, the carve-outs to check, and the evidence an auditor will actually accept.
The checklist
1. Extract the billing history
Pull one row per reading or bill line: account reference, MPAN, date, actual/estimated indicator, consumption, and optionally unit rate and standing charge. Twelve months of history per MPAN is the minimum for meaningful detection.
2. Confirm reading types are reliable
Check how your billing system records customer-own-reads, deemed reads and smart reads. Anything treated as 'estimated' that is not, or vice versa, distorts every downstream control.
3. Flag estimates issued after an actual read
For each account, where a valid actual reading exists and a later bill is estimated, that bill is a triage candidate under SLC 21B. Expect a deliberate over-sensitivity here — the rule cannot see failed meter-reading attempts or appointment history.
4. Review accounts with no actual read in 12 months
Any account still being charged with no actual reading in the last 365 days is an SLC 21B review flag. It is not an SLC 21BA finding. Test SLC 21BA separately using bill date, consumption period and validated-versus-billed consumption.
5. Review carve-outs before concluding anything
Back-billing protection does not apply where the delay is attributable to the customer (obstructed access, refused appointments) or to theft of energy. Every flag must be checked against those facts by your own team.
6. Quantify the £ exposure
For an evidence-qualified SLC 21BA review, price only the positive validated-versus-billed consumption difference, add standing charge for applicable days and apply the validated VAT treatment. Otherwise show 'not quantified'.
7. Seal the evidence
The output should be a report an auditor, Ombudsman case handler or board member can re-verify: anonymised identifiers, masked MPANs, and a SHA-256 hash chain linking the report to the exact file analysed.
Where these audits fail
Sampling that never reaches the long tail
Manual sampling tends to re-check the same accessible accounts. The accounts with 18 months of estimates are usually the ones nobody looks at.
Spreadsheets as evidence
An edited cell is invisible. If you cannot prove the figures were not changed after review, the evidence is weak regardless of how accurate it is.
Conflating triage with breach
An estimate after an actual read is a review candidate, not a breach. Treating flags as findings — or ignoring them because they are not findings — both fail audit.
No owner for carve-out review
SLC 21BA carve-outs (customer obstruction, theft of energy) need a named reviewer with access to appointment and access history. Without one, flags sit unresolved.
Common questions
- What does SLC 21B actually require?
- Standard Licence Condition 21B requires a supplier to base a customer's bill on an actual meter reading where it holds one or can reasonably obtain one. An estimated bill issued after a valid actual reading is the classic exception pattern an auditor looks for.
- What data do I need to audit estimated billing?
- At minimum, per account: an account identifier, the MPAN, the date of each reading or bill line, whether each reading was actual or estimated, and the consumption billed. Pricing fields (unit rate, standing charge) are needed only if you want to quantify the £ exposure.
- How often should we audit?
- Annually is a floor, not a target. Suppliers with a high estimated-reading population tend to sample quarterly. An SLC 21B reading-pattern flag does not itself establish SLC 21BA exposure, which requires separate billing-period and under-billing evidence.
- What evidence survives an audit?
- A report whose inputs and outputs cannot be edited after the fact. A spreadsheet can be changed silently; an evidence report with a cryptographic hash chain can be re-verified by anyone, at any time, against the original file.
Important
This checklist is a plain-language working aid, not legal advice, and it does not determine whether any licence breach has occurred. The licence conditions and Ofgem guidance are the authoritative source. Related reading: back-billing rules (SLC 21BA) explained.
Run this checklist against your own data
PowerView applies steps 3, 4 and 6 automatically to a billing CSV and returns a sealed, verifiable evidence report. Free Risk Check on up to 200 rows, results in 48 hours — the full rule set is published on the methodology page before you send anything.