Warm Home Discount has no receipt rate, so every qualifying household gets the rebate #2615

What is missing

warm_home_discount (added in #2504, still open) pays the £150 rebate to every household in England and Wales that the model has receiving a qualifying benefit. It has no Warm Home Discount receipt rate. The benefits' own take-up carries through, but nothing allows for qualifying households that are never matched to a supplier account or are not named on the electricity bill.

On Microcosm UK 2024-25 (release a133f37a) at #2504's head (20b0384), the model pays £1.024bn in 2025-26 and £1.037bn in 2026-27, to 6.83m and 6.91m households. The 2026 impact assessment expects £806m a year of England and Wales core group spend from 2026-27, around 5.4m rebates.

Evidence

Impact assessment for SI 2026/389. DESNZ, Continuing the Warm Home Discount 2026-2031: final stage impact assessment (DESNZ002(F)-26-EAC, 30 January 2026):

• Para. 38: "Not all people in receipt of means-tested benefits (MTBs) will go on to receive a WHD rebate. To be eligible for the rebate, the benefit recipient or their partner / spouse / DWP-appointee must be named on their energy bill".
• Para. 39: some households fail the data match between DWP and supplier records and are sent a letter asking them to call a helpline.
• Para. 40: "Out of the 8.3m households estimated to receive a qualifying means-tested benefit in GB, it is estimated that around 5.9m will go on to receive a rebate. This estimate is based on delivery experience of the current scheme, which shows that around 85% of pension credit recipients become WHD recipients, compared to around 70% for all other means-tested benefits."
• Table 4: 5.4m expected recipients in England and Wales. Table 7: England and Wales core group spend £806m a year, 2026-27 to 2030-31 (£806m / £150 = 5.37m rebates).
• Table 8 applies the same 85% and 70% to Scotland's new core group. Para. 105 and Table 13 use 70% as the central overall conversion rate, with 60% and 80% as sensitivities.

Scheme statistics. Ofgem's annual report for scheme year 14 (2024-25, page 10): 866,000 Core Group 1 rebates (Pension Credit Guarantee Credit) and 2,271,378 Core Group 2 rebates in England and Wales. Core Group 2 then also required a high-cost-to-heat test, so these counts are not a receipt rate on their own, but they are the delivery record the 85% and 70% come from. The 2026 regulations replace the two groups with a single data-matched core group, so the group split now matters only for the receipt rate.

Proposed approach

Follow the model's existing seeded-draw pattern (uc_deduction_random_draw and uc_has_deduction):

• Parameters gov.ofgem.warm_home_discount.receipt_rate.pension_credit (0.85) and .other_benefits (0.70), from para. 40, in force from 2025-26.
• warm_home_discount_random_draw (Household): a splitmix64 hash of household_id in representative data, 0 in single-household simulations so calculators still show the rebate.
• would_receive_warm_home_discount (Household): the draw is below the Pension Credit rate if any benefit unit receives Pension Credit, otherwise below the other-benefits rate.
• warm_home_discount multiplies by it.

Expected effect: about 1.26m Pension Credit households × 85% plus 5.65m other households × 70%, about 5.0m rebates or £0.75bn in 2026-27, against the impact assessment's £806m.

Open questions:

• The rates are delivery experience, not law. They could sit under gov.simulation (as the UC deduction parameters do) rather than gov.ofgem.
• A household with both Pension Credit and another qualifying benefit gets the Pension Credit rate.
• The qualifying date in the regulations is still not modelled.

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