Scottish Two Child Limit Payment is in effect from 2025-04-06 but the scheme was never enacted

Summary

gov.social_security_scotland.two_child_limit_payment.in_effect is true from 2025-04-06, so two_child_limit_payment pays the UC child element for every limit-affected child in a Scottish benefit unit during 2025-26. The Scottish Government's Two Child Limit Payment was never enacted: the regulations were not laid after the UK government announced on 26 November 2025 that the two-child limit would be removed, and no payments were made. For 2026-27 onward the variable happens to compute zero because the UC limit itself is repealed from 2026-04-06 (gov.dwp.universal_credit.elements.child.limit.child_count → inf), but any 2025-26 simulation for Scotland pays a benefit that did not exist.

What the model does today (main, 2.97.0)

• policyengine_uk/parameters/gov/social_security_scotland/two_child_limit_payment/in_effect.yaml: 0001-01-01: false, 2025-04-06: true (commit ca8ff982 "Remove end date from Two Child Limit Payment in_effect parameter", 2026-01-09).
• policyengine_uk/variables/gov/social_security_scotland/two_child_limit_payment.py: in_scotland * in_effect * affected_children * uc_child_amount * 12, where affected_children sums uc_is_child_limit_affected over the benefit unit.
• uc_is_child_limit_affected is nonzero throughout 2025-26 (the limit still applied), so the payment is live for that year. The variable feeds household_benefits / net income for Scottish households.

What actually happened

• The Scottish Government's payment was planned to launch on 2 March 2026 with a first payment covering the year. After the UK announcement of 26 November 2025, the Scottish Government told the Scottish Commission on Social Security that the regulations would not be laid: https://socialsecuritycommission.scot/publications/draft-regulations/the-two-child-limit-payment-scotland-regulations-2026/the-two-child-limit-payment-scotland-regulations-2026-further-update-from-the-scottish-government/ (3 December 2025).
• Scottish Budget 2026-27, Chapter 5, Table 5.08 (Social Security Assistance) carries the Two Child Limit Payment line with a footnote that the funding "is no longer required. The £11.3 million allocated in 2025-26 will be removed at Spring Budget Revision": https://www.gov.scot/publications/scottish-budget-2026-27/
• The UK removal is the Universal Credit (Removal of Two Child Limit) Act 2026 (Royal Assent 18 March 2026), effective for assessment periods from 6 April 2026: https://bills.parliament.uk/bills/4059 . The model already carries this.
• Scale if the parameter is exercised: the Scottish Fiscal Commission costed the scheme at £155m for 2026-27 (43,000 children): https://fiscalcommission.scot/mitigating-the-two-child-limit-and-the-scottish-budget/ . A full 2025-26 year at the UC child element would be of the same order.

Impact

• Every 2025-26 Scottish household or population run overstates benefit income for families with three or more children on UC, and understates 2025 child poverty in Scotland relative to what happened.
• Datasets calibrated to 2025 (the microcosm UK dense/local line uses calibration year 2025) inherit the phantom payment in their engine outputs.

Suggested fix

• Set in_effect to false throughout (drop the 2025-04-06: true value), or delete the value and leave the parameter as a reform switch, so two_child_limit_payment is zero under current law in every year. Keep the variable so a contributed reform can turn the scheme on as a counterfactual.
• Update the YAML tests added in #1465/#1466 so the 2025 cases expect zero under baseline and the positive cases run under a reform that sets in_effect: true.
• Add the SCoSS update and the Budget 2026-27 footnote to the parameter's reference list.

Inspect policyengine_uk/parameters/gov/social_security_scotland/two_child_limit_payment/in_effect.yaml and the tests added in #1465/#1466; compare the baseline and reform cases with the variable in policyengine_uk/variables/gov/social_security_scotland/two_child_limit_payment.py. Done means baseline 2025 cases produce zero, positive cases work when the reform switch is enabled, and the parameter references include the cited SCoSS update and Budget 2026-27 footnote.