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SLC 21BA - 12-month backbilling limit.

SLC 21B - Billing based on meter readings.

Domestic customers, and microbusiness customers where the supplier applies the same backbilling protection. Non-microbusiness I&C accounts are out of scope.

SLC 21BA: IF a bill or correction includes a positive under-billed consumption difference for an evidenced consumption period ending more than 12 months before the bill date THEN flag it for SLC 21BA review.

SLC 21B: IF no actual reading exists for 365 days, OR an actual reading exists and a later bill is based on an estimated reading, THEN create an SLC 21B review flag. This does not establish financial exposure.

account_ref (or mpan) - account identifier

mpan - supply point number

reading_date - date of the reading / bill line

reading_type - actual or estimated

consumption - kWh on the line

unit_rate - £/kWh (optional; falls back to the published cap)

standing_charge - £/day (optional)

bill_date - issue date of the bill or correction (required for SLC 21BA)

consumption_period_start / consumption_period_end (required for SLC 21BA)

validated_actual_consumption and cumulative_consumption_billed (required for SLC 21BA)

fuel_type, customer_type and vat_rate (required to validate VAT treatment)

standing_charge_days - applicable chargeable days

Indicative screening estimate = ((validated actual consumption - cumulative consumption already billed) × unit rate + standing charge × applicable days) × (1 + applicable VAT). It is calculated only for an evidenced consumption period ending more than 12 months before the bill date. If dates, consumption difference, tariff or VAT treatment are missing, the value is not quantified.

Every flag opens as 'potential exception - needs supplier review'. Nothing is auto-closed, auto-refunded or reported to any regulator by this app. The supplier confirms, dismisses or escalates each row against its own billing records.

SLC 21BA carve-outs are not modelled: back-billing protection does not apply where the delay is attributable to the customer (obstructed access, refused appointments), to theft of energy, or to other conduct outside the supplier's control. Flags must be reviewed against those facts.

SLC 21B allows an estimated bill where an actual reading could not reasonably be obtained. The engine cannot see meter-reading attempts, appointment history or industry data flows, so estimate-after-actual flags are deliberately over-sensitive and are triage candidates, not findings.

The engine cannot determine customer-fault carve-outs, theft, meter-access evidence, change-of-tenancy or change-of-supplier facts. Those facts require supplier review even when the structured billing fields support an SLC 21BA screening flag.

Reading type is derived from the text in the file: anything containing 'est' is treated as estimated, everything else as actual. Customer-own-reads and deemed reads are not distinguished.

Detection and triage only. It does not replace regulatory judgement.

Tested on sample data only. Not yet tested against real billing records, and not yet subject to an independent energy-regulatory review. Both are prerequisites we state openly before any supplier relies on the output.