Model Winter Fuel Payment high-income recovery separately from entitlement

Problem

winter_fuel_allowance currently treats the November 2025 taxable-income threshold as an eligibility condition: pensioners above the threshold receive no WFA in the benefit variable.

That conflates two surfaces:

• Payment entitlement / amount: The Social Fund Winter Fuel Payment Regulations 2025 reg. 2 entitles a person to a Winter Fuel Payment if they have reached pensionable age by the qualifying week and are ordinarily resident in England or Wales. Reg. 3 then sets the payment amounts (£200/£300 ordinary amounts, with smaller shared-household/residential-care branches). I do not see a £35,000 taxable-income eligibility test in the 2025 WFA regulations.
• High-income recovery: Policy materials describe recovery from pensioners with taxable income over £35,000 who receive WFPs and must repay. That sounds like a tax/recovery charge, not non-entitlement to the payment.

Closed issue #1387 asked to "implement tax clawback mechanism", but the closing comment says the baseline now uses a £35,000 taxable-income threshold for WFA eligibility. That likely gives the same net income for some high-income households, but it misstates the WFA payment variable and government spending/tax decomposition.

Suggested behavior

Keep winter_fuel_allowance as the gross WFA payment entitlement under the 2025 regulations, and model any £35,000 high-income recovery as a separate tax/recovery variable or income-tax component. Then HBAI net income can subtract the recovery without zeroing out the benefit itself.

References

• Social Fund Winter Fuel Payment Regulations 2025, regulation 2: https://www.legislation.gov.uk/uksi/2025/969/regulation/2/made
• Social Fund Winter Fuel Payment Regulations 2025, regulation 3: https://www.legislation.gov.uk/uksi/2025/969/regulation/3/made
• Existing issue: #1387

Start by locating the implementation of the winter_fuel_allowance variable and reviewing closed issue #1387. Compare its current threshold behavior with regulations 2 and 3 in the linked 2025 references. Done means the variable represents gross entitlement, with any high-income recovery modeled separately and covered by tests for both payment and recovery.