Count Carer Support Payment as Council Tax Reduction income

[MaxGhenis]

Fixes #1955

Stacked on #1952. This branch contains #1952, merged with main at da947ee6. Review only the commits after b4d613a8. Retarget or rebase once #1952 merges. #1952 makes carer_support_payment the Carer Support Payment component only and moves the Scottish Carer Supplement into scottish_carer_supplement. Adding carer_support_payment to the CTR list is correct only once that split is in.

What changes

council_tax_reduction_applicable_income listed carers_allowance but not carer_support_payment. In 2025 the model moves Scottish carers from Carer's Allowance (CA) to Carer Support Payment (CSP), so from then on their CTR income left out their carer's benefit. This PR adds carer_support_payment to the list. scottish_carer_supplement stays off.

Law

Read from legislation.gov.uk (CLML, valid from 2026-04-01; fetched 2026-09-30, independent re-check from fresh fetches pending):

• Working age. Council Tax Reduction (Scotland) Regulations 2021 (SSI 2021/249) reg 57(1): "An applicant's unearned income is any of their income ... falling within the following descriptions", including (b)(iva) "carer support payment". SSI 2023/258 inserted it on 19.11.2023. Reg 4 defines it as "the Carer Support Payment component of Carer Support" (SSI 2025/340, from 15.3.2026). The list is closed and does not name the Scottish Carer Supplement. Sch 4 para 24(e) disregards the supplement as capital for 52 weeks.
• Pension age. Council Tax Reduction (State Pension Credit) (Scotland) Regulations 2012 (SSI 2012/319) reg 27(1)(j) counts "social security benefits other than" a list. CSP is not on the list. (xxi) excepts the Carer's Allowance Supplement. (xxia) excepts the Carer Additional Person Payment, and (xxib) "the Scottish Carer Supplement component of Carer Support"; both were inserted on 15.3.2026 by SSI 2025/340 sch 1 para 8(3). Reg 2(1) defines CSP as the component.
• No disregard of CSP above the CA amount. DWP instruments have one: SPC Regs Sch IV para 19, HB Regs Sch 5 para 74, and the UC reg 66 cap. Searching the whole of both Scottish instruments for "in excess of the amount" finds no hits. Every "carer support payment" hit is the income head, a definition, or a carer, severe disability or earnings-disregard condition. CSP therefore counts in full. At 2026-27 rates CSP and CA are both £86.45, so a cap would not bind anyway.
• Tax. Both instruments deduct income tax only from earnings: SSI 2012/319 reg 33(2)(a)(i) and reg 36; SSI 2021/249 Part 6 Chapter 3. Benefits count gross. In law, then, the supplement has no effect on Scottish CTR. The model deducts a family's whole income tax from CTR income. That approximation predates this PR and the shared variable uses it for every scheme. In the model, therefore, the taxable supplement reaches CTR income through income tax and only through it. Chip filed to deduct only earnings tax, matching Take Housing Benefit earnings disregards from net earnings only #1908 for HB.
• England and Wales. The model pays CSP only to Scottish households (carer_support_payment requires country == SCOTLAND), so the shared list cannot change CTR there. (What the English and Welsh instruments say about CSP: pending.)

Rates (weekly): CSP £86.45 and SCS £11.70 from 5.4.2026 (SSI 2023/302 reg 16, as amended by SSI 2026/170 reg 12(3)); CSP £83.30 in 2025-26; SCS £11.29 from 15.3.2026 to 4.4.2026 (SSI 2025/340).

How PolicyEngine models Scottish CTR

simulated_council_tax_reduction_benunit runs one national scheme for Scotland, at working age and pension age alike. It has a maximum support rate of 1, a £16,000 capital limit, and withdrawal at 20% of income above the applicable amount (gov.local_authorities.scotland.council_tax_reduction). It uses the HB applicable amounts and premiums, including the carer premium, and this shared income variable. Draft #1966 will move Scottish and Welsh working-age claims onto their own income and UC rules. Its council_tax_reduction_working_age_unearned_income already lists carer_support_payment, but it then subtracts supplement / (rate + supplement) of it, on the assumption that carer_support_payment still includes the supplement. Once #1952 lands, that subtraction removes £535.88 a year (4,495.40 × 11.70 / 98.15) of genuine CSP in 2026. Whichever of #1952 and #1966 merges second must drop it; I've left a note on #1966. After #1966, this PR's change still governs Scottish pension-age CTR, England pensioners and the English councils.

Household examples (2026 unless stated; council tax £2,000; YAML cases)

Case	CTR income, before → after	CTR, before → after
Single carer aged 40, Scotland, private pension £7,000, no UC	7,000 → 11,495.40 (+86.45 × 52)	2,000 → 1,195.40 = 2,000 − 0.2 × (11,495.40 − 7,472.40)
Same carer in Wales, on CA (control)	11,495.40 → 11,495.40	1,195.40 → 1,195.40
Same Scottish carer, 2025 (CSP £83.30, no supplement)	7,000 → 11,331.60	2,000 → 1,173.25
Same Scottish carer, 2024 (still on CA £81.90)	11,258.80 (unchanged)	1,163.68 (unchanged). On main the award jumps to 2,000 when CA turns into CSP in 2025; it no longer does.
Pensioner carer aged 70, Scotland, private pension £14,000	12,732.91 → 17,228.31. The supplement adds only its £121.68 of tax	2,000 → 1,717.50
Pensioner couple, partner a carer, Scotland, pensions £12,000 + £6,500	18,500 → 22,995.40	2,000 → 1,888.52

Every row is a YAML case. The "before" figures come from running the same cases on the parent commit, which leaves CSP out of CTR income.

Tests

• council_tax_reduction_carer_support_payment.yaml has 10 cases, each worked from statutory rates with the arithmetic in comments. On the parent commit 6 fail, every one on council_tax_reduction_applicable_income (for example "7000 differs from 11495.40"). The 4 controls pass on both: Wales on CA, a Scottish carer who does not claim, 2024 on CA, and an English pensioner. On the branch all 10 pass. The full YAML suite passes on the branch: 1,352 passed.

• test_council_tax_reduction_carer_income_properties.py holds 3 Hypothesis properties. Each draw is a family in Scotland in 2026, single or couple, working-age without UC or pension-age, carer by hours or by a reported award. Each family runs on a private-pension grid from £0 to £40,000, with and without the claim.

  1. Counts the component. Claiming CSP raises CTR income, before tax and NI and apart from the other counted benefits, by exactly 86.45 × 52. The award never rises. Where both awards are partial it falls by 20% of the rise in income.
  2. Invariant to the supplement except through income tax. Setting gov.social_security_scotland.carer_support_payment.supplement to 0 leaves CSP and every other counted benefit unchanged, and leaves CTR income plus income tax unchanged. The award never falls because of the supplement. Where both awards are partial it rises by exactly 20% of the tax on the supplement.
  3. Differential against Housing Benefit. Where Guarantee Credit does not passport HB, HB applicable income before its disregard, childcare element and tariff income equals CTR income. This holds in England, Wales and Scotland. HB already counts CA and the CSP component.

  On the branch: 3 passed (133 s). On the parent commit: properties 1 and 3 fail; 2 passes, because the parent counts neither CSP nor the supplement. The minimal counterexample is a single 25-year-old Scottish carer with a reported award and no income, whose CTR income rises by 0 instead of 4,495.40.

  Mutation check, in a scratch worktree that also lists scottish_carer_supplement: 5 YAML cases fail, each by exactly 608.40 (11.70 × 52), and the property run on the mutant is pending.

• Full pytest policyengine_uk/tests/ on the branch: pending.

Invariants (hold for every input in the drawn domain): conservation (property 1); a metamorphic relation over the supplement (property 2); a differential identity with HB (property 3); monotonicity of the award in the carer's benefit (properties 1 and 2). They compare the model's own measures, so they hold whatever carer's benefit the model pays.

Enhanced FRS impact

These are real microsimulation runs: the parent commit b4d613a8 against this branch, on the published Enhanced FRS 2024-25 (policyengine-uk-data-private tag 1.57.4, enhanced_frs_2024_25.h5, sha256 03fe15e4…). That is 2 runs, each covering 2025-2030. Totals are summed in float64.

Year	CTR total (parent)	Change in CTR	Benefit units with CSP (sample)	…of which on CTR (parent)
2025	£2,305.0m	−£0.13m	113.0k (98)	1.04k (3)
2026	£2,360.3m	−£0.38m	113.4k (98)	1.04k (3)
2027	£2,425.1m	−£0.68m	113.8k (98)	1.05k (3)
2028	£2,490.2m	−£0.71m	114.3k (98)	1.05k (3)
2029	£2,555.3m	−£0.05m	114.8k (98)	0.07k (2)
2030	£2,617.2m	−£0.05m	115.3k (98)	0.07k (2)

2026 detail:

• CTR income. It rises by £508m across 96 sample benefit units (113k weighted), all in Scotland: 64.5k working age and 48.4k pension age. Where the zero floor does not bind, the rise equals each unit's CSP to within £0.003. Units without CSP change by exactly £0.
• The award. It changes for only 3 sample benefit units (1,044 weighted), all Scottish and working age, by −£369 on average. All 3 lose CTR entirely: one couple on UC (weight 976), and two couples in which both members receive CSP.
• Why the dataset effect is small.
  • Only 18 of the 98 CSP units (21k weighted) would claim CTR in the data. would_claim_council_tax_reduction is reported CTR or claims_all_entitled_benefits.
  • None of the 10 pension-age CSP units claims.
  • Most of the claimants already had income above the applicable amount. The national scheme counts UC as income, which Give Scotland and Wales working-age council tax reduction their own rules (UC routes, passport, child amounts) #1966 replaces with the Scottish UC rules.
• Unchanged. HB, UC, Pension Credit, poverty (BHC and AHC) and every English, Welsh and Northern Irish figure. Household net income and HBAI net income fall by exactly the CTR change.

The scripts (dataset_impact.py, compare_impact.py) and their outputs are kept outside the repo.

Axiom

axiom: pending (state of rulespec-uk for SSI 2021/249 reg 57 and SSI 2012/319 reg 27 being established).

Interactions with other open PRs

• Count Carer's Allowance and Carer Support Payment as Pension Credit income #1952 (parent). Must merge first.
• Give Scotland and Wales working-age council tax reduction their own rules (UC routes, passport, child amounts) #1966. Remove its supplement-share subtraction once Count Carer's Allowance and Carer Support Payment as Pension Credit income #1952 is in; see above.
• Carers overlapping-benefits branch (carers-overlapping-benefits, Carer's Allowance and Carer Support Payment ignore the overlapping-benefit reduction by State Pension #1953, not yet pushed).
  • It makes carer_support_payment the CSP payable after CSP Regs reg 16(2), and adds carer_support_payment_pre_overlap.
  • SSI 2012/319 reg 27(5) lists the Overlapping Benefits Regs 1979 but not CSP Regs reg 16(2). Under reg 27(3) a benefit is counted "before the deduction". Pension-age Scottish CTR may therefore need the pre-overlap amount. (Legal re-check pending.)
  • Whichever merges second reconciles.
• Count contributory ESA, Maternity Allowance, industrial injuries benefit and capped Carer Support Payment as UC unearned income #1958 (UC reg 66). No overlap with this PR.

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