Charge in-unit non-dependants in the local Council Tax Reduction schemes

[MaxGhenis]

Stacked on #2017 (in-unit-non-dep-deductions), for issue #2014. #2017 charges non-dependants inside the claimant's own benefit unit in UC, HB and the national CTR schemes, and keeps the five English working-age local schemes on their old aggregation behind a mask. This PR brings those schemes (Merton, Kingston upon Thames, Newham, Westminster, Oxford) into line with the law and with #2017's national variable.

The law

Each council's 2026-27 scheme reproduces the Default Scheme's (SI 2012/2886) definitions:

• Merton, Kingston upon Thames and Newham: paras 4, 6 and 9 and the working-age deduction paragraph (30, 30A, 30B).
• Westminster: its summary says the Default Scheme is the basis, and its Appendix A gives the 2026-27 scale.
• Oxford: paras 42-47 and the Annex 1 glossary.

What follows from the texts:

• Who is a non-dependant. Anyone who normally resides with the applicant (para 9), except:

  • a member of the applicant's family (para 6: the partner, or a child under 16 or qualifying young person the applicant is responsible for);
  • a joint occupier;
  • a commercial lodger;
  • a charity-engaged carer.

  So an adult in the applicant's own benefit unit who is not the partner, a child or a qualifying young person is a non-dependant (a 19-year-old who has left education, say, or an adult son). So is each adult in another family. Westminster's guidance agrees ("anyone over 18 living in your home"; partners and children the claimant gets Child Benefit for excepted). So does Oxford's glossary.

• Banding (para 30(1)-(2), para 10). A non-dependant aged 18 or over is banded on his normal gross weekly income, if in remunerative work on their own hours. For a couple, regard is had to the couple's joint income (para 30(4); Oxford para 44).

• Couples (para 30(3)). A couple pays one deduction, the higher of the two. Merton and Kingston upon Thames add "(other than where there is an award of universal credit)"; Newham's 30B(3), Westminster and Oxford have no such exception.

• Joint occupiers (para 30(5)). A non-dependant of two or more jointly liable people is apportioned equally between them.

• Exemptions (para 30(8)). Being "on income support, state pension credit, an income-based jobseeker's allowance or an income-related employment and support allowance", or entitled to UC calculated on no earned income, exempts the person on the award. Oxford applies these to pensioner applicants only (para 47), as before.

Every 2026-27 deduction parameter for the five councils matches its scheme text.

Changes

policyengine_uk/variables/gov/local_authorities/council_tax_reduction/_legacy.py:

• local_non_dep_deductions now has the same shape as Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's council_tax_reduction_non_dep_deductions: claims × joint-liability share × (the household's pool of non-dependant deductions, less the claiming family's own claimant, partner and children). The pool counts:

  • the higher member of each non-dependant couple (each member in Merton and Kingston upon Thames when the couple has UC);
  • every other eligible person separately.

  It replaces "the household total minus the family's own maximum", which never charged the applicant's own in-unit non-dependants. It also drops Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's temporary in_other_non_liable_family mask from the aggregation. Eligibility still uses that helper.

• normal_gross_income_non_dep_deduction now:

  • bands a claimant or partner on the couple's joint gross income and anyone else on their own, not on the whole benefit unit's income;
  • uses each person's own hours, not the benefit unit's maximum;
  • gates the income-related benefit and UC exemptions to the award's claimant and partner;
  • computes the UC limb on the couple's earned income.

These are #2007's fixes 1 and 3 (couple-only joint income; benefit-receipt exemptions gated to the claimant and partner), carried into the local schemes. They use the same names and semantics as the composition branch in-unit-non-dep-deductions-on-2007.

#2017's Newham case "a jointly liable sharer does not bear the head's own in-unit son" pinned the temporary mask. It now apportions the son's £979.68 half to each jointly liable family (para 30(5)), as #2017's national variable already does.

Open interpretation, flagged with #2007's author. Para 30(8)(c) exempts a non-dependant "entitled to an award of universal credit where the award is calculated on the basis that the person does not have any earned income". This PR reads a joint award on the couple's earnings (today's local behaviour). #2007 reads it on each person's own earnings for the national schemes and HB. Neither of us found guidance that settles it. It only binds for a non-dependant UC couple where exactly one member earns.

Review r1 fixes (head 663a5b7)

An independent review (Subfleet, Opus) of 570f163 requested changes. This head addresses all three findings.

1. Personal exclusions (major). Para 9(2)(d)-(e) exclude the person, whatever family they are in. Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's in-unit term let through two people:

   • an adult who personally pays the householder as a boarder or lodger;
   • an adult who is personally a joint tenant.

   Removing the local mask exposed this for the local schemes. Eligibility (council_tax_reduction_individual_non_dep_deduction_eligible, shared with the national schemes) is now (other family | in-unit) & ~personally_excluded, where personally_excluded covers:

   • the household head (the person liable for the council tax, LGFA 1992 s.6);
   • anyone liable for the household's rent;
   • anyone paying rent as a boarder or lodger.

   A lodger's adult son who doesn't pay the householder himself is still a non-dependant, and a YAML case pins that.

2. The applicant charged for themself (major). A household head whom the claimant/partner inference left outside his benefit unit's couple was an "in-unit non-dependant" of his own claim. The household-head exclusion above fixes this, and a YAML case pins it.

3. Oracle independence (minor). Property 6 now derives who claims and each claim's joint-liability share from the generated structure (legal_claims_and_shares). It asserts the model's match, so injected claim or share errors fail it.

The three new exclusion cases fail on 570f163 and pass here.

Effect on the national schemes. Real Microsimulation, enhanced FRS 2024-25 (uk-data 1.57.4), 2026, 570f163 → 663a5b7:

• The intermediate council_tax_reduction_non_dep_deductions falls from £16,617.5m to £13,200.5m, on 374k benefit units (135 survey households).
• Every person whose deduction changed is a claimant or partner: 369k household heads (134 survey households) and 267k others (54).
• A claimant or partner is not an in-unit adult, so under Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017 these people were eligible only through the "other non-liable family" proxy, which compares against the oldest adult's family. So these are household heads, and their partners, in a family other than the oldest adult's, who were charged as non-dependants of the oldest adult's family. As the people liable for the council tax they are nobody's non-dependants.
• Who claims in those households is Give Council Tax Reduction to the household head's family, not the oldest adult's #2009's fix.
• No award changes: household council tax reduction, net income and poverty are unchanged.

Invariants

For every input:

1. Oracle. Each council's individual and family deductions equal an independent calculation from its 2026-27 scale (Hypothesis property 6). Every other council's variables are zero.
2. Independence. The earnings of an adult who is not a claimant or partner change no one else's deduction (property 7).
3. Conservation. Across jointly liable applicants, each non-dependant's deduction is borne once in full (by claims × share). Property 6's oracle implies this.
4. No self-charge. A claiming family is never charged for its own claimant, partner or children. Asserted by Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's eligibility property and the oracle's own-family subtraction.

Properties 6 and 7 both fail on #2017's head (the previous aggregation), so they bind. Property 7 adds a guaranteed binding family to every generated household.

Tests

• New YAML (local_scheme_non_dependants.yaml, 23 cases, including the review r1 counterexamples): each council's own in-unit son, a lone parent plus her working son in another family, gated Income Support, JSA and UC exemptions, Merton's UC couple on its own hours, a joint-income couple, the applicant PIP exemption, a full-time student, a 19-year-old who has left education, and Oxford's pensioner-only exemptions. Every expectation is hand-computed from the scheme text.
• Local and in-unit YAML suites: 95 passed (gov/local_authorities, benefit_unit_non_dependants.yaml).
• Property tests: all six pass, the four existing and the two new.

Impact

Real Microsimulation of the released enhanced FRS 2024-25 (uk-data 1.57.4, sha256 03fe15e40a4c), 2026, #2017 head 270412d → 570f163:

• no change to any household;
• council tax reduction £2,360.32m in both runs;
• household net income and poverty unchanged.

Every enhanced-FRS household has local_authority = MAIDSTONE (the variable's default; the dataset carries no local authority), so the five local schemes never run on survey data. The fix changes household-level calculations in those councils only.

Axiom

axiom: TheAxiomFoundation/rulespec-uk#426 queued. The Kingston upon Thames, Merton and Newham modules derive each non-dependant's deduction from their own income and hours, which is encoded-correct given its inputs. They take who is a non-dependant, the exemption and the household total as inputs. Westminster defers Appendix A, and Oxford has no module.

Coordination

• Assess each Council Tax Reduction claim under its own family's scheme and exemption #2015 (ctr-per-family-scheme) rewrites the same two helpers. Whoever lands second, the agreed resolution is:
  • where(applicant_exempt, 0, claims * share * non_dependants);
  • Assess each Council Tax Reduction claim under its own family's scheme and exemption #2015's in_scheme_area for working_age;
  • drop claimant_exempt;
  • keep this PR's couple and own income, own hours and gated exemptions.
• Give Council Tax Reduction to the household head's family, not the oldest adult's #2009 changes council_tax_reduction_claimant_benunit, which the pool reads. Its eligibility line follows Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's resolution.
• Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007 doesn't touch _legacy.py.

🤖 Generated with Claude Code

[vahid-ahmadi]

Thanks Max. The rules applied match each scheme:

• Who is a non-dependant: charging in-unit adults follows para 9 ("any person ... who normally resides with an applicant", except "any member of the applicant's family").
• Couples: one deduction, the higher, on joint income follows para 30(3)-(4).
• Joint liability: the apportionment follows para 30(5).
• Merton and Kingston: the per-member UC deduction matches the Default Scheme's own "(other than where there is an award of universal credit)".

Verified at 663a5b7:

• Tests: the local_authorities YAML passes 67/67, benefit_unit_non_dependants 28/28 and properties 6/6.
• Probe for Newham, 2026:
  • The household: a grandmother aged 55 applies alone. A 19-year-old couple live with her as another family; the father earns £30,000 and works 37.5 hours.
  • The deduction is £1,175.72 (£22.61 × 52 on joint income of £576.92 a week). The mother's own deduction, £392.08, is the lower, so it is not taken.
  • CTR is £84.28.

1. Blocking: needs a rebase. #2017 conflicts with main in 6 files, and this PR adds a seventh, _legacy.py (from #2009, merged 4 Oct). This is the same standard as #2015 and #2078. #2030 is also stacked on #2017.
2. Should fix: #2027 is missing from Coordination, and the conflict at _legacy.py:175-179 changes amounts.
   • The case: Merton, a non-dependant couple. One reports £5,000 of income-related ESA; the other works 20 hours on £15,000.
   • Here: no deduction, CTR £1,800.
   • With #2027's is_on_*: £551.20 deducted, CTR £1,248.80.
   • Default Scheme para 2(4) ("payable to him") with para 30(3) supports #2027.
   • Take #2027's is_on_* there, keep your claimant-or-partner gate on the Pension Credit (:179) and UC limbs, and add the case.
3. Should fix: this does not fix the #2078 grandmother cases.
   • Both own_family_member (_legacy.py:114) and in_unit (council_tax_reduction_individual_non_dep_deduction_eligible.py:40) key on is_claimant_or_partner.
   • So when the head applies alone and the inference makes the 19-year-olds the unit's couple, they count as neither her family nor her non-dependants.
   • Put my probe household in one benefit unit and this PR gives a £0 deduction. Under paras 6 and 9 it should be £1,175.72, giving CTR of £84.28.
   • Whichever PR lands second should key both on is_council_tax_reduction_applicant_or_partner from #2015/#2078.
   • #2078's Newham and Kingston grandmother cases also need explicit inputs:
     • set the young father's weekly_hours, so the hours band applies;
     • set current_education for the 19-year-olds, who otherwise default to tertiary education and fall under the full-time student exemption (para 30(7)(c)).
     • Without these, those cases give a £0 deduction whatever the non-dependant logic does.
4. Should fix: the agreed #2015 resolution covers _legacy.py but not the eligibility file.
   • #2015 rewrites that test as ~claimant_benunit & ~benunit_is_rent_liable, which drops in_unit.
   • Keep (other_family | in_unit) & ~personally_excluded, and put #2015's claimant-benefit-unit test inside other_family.
5. Should fix: the review-1 fix changes council_tax_reduction_individual_non_dep_deduction_eligible, which the national schemes share. That is the body's −£3.4bn on the intermediate.
   • Say so in the title and changelog: changelog.d/2014-local.fixed.md mentions only the local schemes.
   • Also remove the survey household counts ("135 survey households", "134", "54").
6. Nit: close relatives who pay board are non-dependants.
   • Para 9(3)(a)(i) makes someone who pays a close relative a non-dependant again: "that person is a close relative of his or his partner".
   • council_tax_reduction_individual_non_dep_deduction_eligible.py:47-51 excludes every boarder and lodger, for example an adult son paying his mother board. Main does the same through in_other_non_liable_family.
   • There is no relationship input, so document the gap in the variable and open a follow-up issue.

[MaxGhenis]

#2062 is now on main (merge commit c4659aa). main has one resolved household head: is_resolved_household_head (Person: the eldest member the is_household_head input flags, else the eldest member) and benunit_contains_household_head (BenUnit, defined from it). No formula outside is_resolved_household_head reads is_household_head, and test_only_the_resolved_head_reads_the_flag in policyengine_uk/tests/test_household_head_agreement_properties.py enforces that.

This PR still adds formulas that read the raw flag:

• policyengine_uk/variables/gov/local_authorities/council_tax_reduction/council_tax_reduction_individual_non_dep_deduction_eligible.py: person("is_household_head", period)

Each needs to read the resolved head instead:

• family level: benunit.any(person("is_household_head", period)) becomes benunit("benunit_contains_household_head", period), and person.benunit.any(person("is_household_head", period)) becomes person.benunit("benunit_contains_household_head", period);
• person level, only where the formula needs the head as a person: person("is_household_head", period) becomes person("is_resolved_household_head", period).

test_only_the_resolved_head_reads_the_flag fails until every such read is moved. Please also add each variable you move to OUTPUTS in that test file, so its metamorphic test (flags matter only through the resolved head) computes it. Test inputs that set is_household_head are fine as they are.

[MaxGhenis]

Cross-reference from #2027 (a maintainer review there, 5 October, raised this household).

#2027 (head 360aef868) changes _legacy.py's non-dependant exemption for Income Support, income-based JSA and income-related ESA from the benefit unit's totals to is_on_income_support / is_on_income_based_jsa / is_on_income_related_esa. A person is on the award when it is payable to them (Default Scheme Sch para 2(3)-(4)); of a couple, only the payee is.

The household: Merton, a non-dependant couple. One reports £5,000 of income-related ESA; the other works 20 hours on £15,000.

• This PR alone exempts both: no deduction.
• With Count only the claimant's and partner's legacy awards in means tests and passports #2027, the payee is exempt and the partner pays £10.60 × 52 = £551.20 on joint income of £288.46 a week (para 30(3), (4)). Count only the claimant's and partner's legacy awards in means tests and passports #2027 now has this as a YAML case (2027, in legacy_award_readers/council_tax_reduction_passports.yaml).

The resolution the reviewer proposed: when this PR merges main after #2027, read is_on_* for the IS, JSA and ESA limbs, and keep this PR's claimant-or-partner gate on the Pension Credit and UC limbs. The conflict will be at _legacy.py around the income_based_benefit block.