Council tax integration: Nuffield Workstream 2 deliverable tracker

Tracking issue for the council tax workstream committed in the Nuffield R&D 2025 application (Workstream 2, "Council Tax Integration", £32,000 / 4 person-months, Year 1 Q1 kickoff).

Application text: https://policyengine.github.io/nuffield-rda-2025

What we promised

We will add council tax to microsimulation, enabling combined local and national tax burden analysis. This addresses a significant gap—existing models omit local taxation despite £40bn annual revenue.

Method committed (test-driven, citing the childcare precedent):

1. Implement council tax bands and local authority rates from MHCLG data
2. Validation test cases
3. Compare against administrative totals
4. Validate distributional impacts

Deliverables committed:

1. Council tax by band and local authority
2. National model integration
3. Validation report
4. Policy examples

Current state

More exists than the deliverable list suggests — the data layer is substantially built, the liability calculation is not.

Already in place:

• policyengine-uk-data: policyengine_uk_data/storage/la_council_tax.csv — 360 LAs (England, Scotland, Wales) with band_d_amount, VOA dwelling counts for bands A–I, and net council tax requirement.
• policyengine-uk-data: band assignment to households in datasets/enhanced_cps.py (_assign_council_tax_bands), using storage/council_tax_bands_2024.csv regional shares.
• policyengine-uk-data: calibration targets ons/council_tax_band_d/{code} and voa/council_tax/{code}/{band} emitted from targets/sources/la_council_tax.py.
• policyengine-uk: the full Council Tax Reduction stack under variables/gov/local_authorities/council_tax_reduction/, with bespoke schemes for Kingston upon Thames, Merton, Newham, Oxford and Westminster, plus England pensioner / Scotland / Wales parameters.
• TheAxiomFoundation/rulespec-uk: the national England pension-age CTR scheme (SI 2012/2885) and 100 local authority CTR schemes encoded with proof citations, plus a 297-row LA registry.

Not in place:

• Council tax liability is not computed anywhere. variables/input/consumption/property/council_tax.py is an input variable whose own docstring says it is "supplied by the household dataset rather than recomputed from local authority council tax schedules". council_tax_band is likewise an input defaulting to Band D.
• No statutory band-ratio parameters (A=6/9 … H=18/9 relative to Band D).
• No council_tax_band_d_amount variable in policyengine-uk, despite the data repo emitting a calibration target against that name (separate issue to follow).
• No discounts, exemptions or premiums: single-person 25%, student/SMI exemptions, empty-home and second-home premiums.
• No parish/precept handling.
• Liability sourcing is England-only — Wales (StatsWales) and Scotland (Scottish Government) band amounts are not sourced.
• No validation against the MHCLG administrative total.

Work items

Deliverable 1 — council tax by band and local authority

• Refresh la_council_tax.csv to MHCLG 2026-27 and extend Band D to all eight bands (Table 9 of Tables_1-9_2026-27.ods gives ONS code + Band A–H for 296 English authorities)
• Alias map for the 12 authorities whose MHCLG name does not exactly match the LocalAuthority enum: Bristol, Cumberland, Durham, Herefordshire, Kings Lynn and West Norfolk, Kingston upon Hull, North Northamptonshire, North Yorkshire, Somerset, St Helens, West Northamptonshire, Westmorland and Furness
• Source Wales band amounts (StatsWales)
• Source Scotland band amounts (Scottish Government council tax datasets)

Deliverable 2 — national model integration

• council_tax_band_d_amount variable
• Statutory band-ratio parameters, including Band I for Wales
• Computed gross liability = Band D amount × band ratio
• Single-person discount (25%)
• Exemptions: students, severe mental impairment, Class A–W exempt dwellings
• Empty-home and second-home premiums
• Decide and document the relationship between computed liability and the existing council_tax input, including the effect on downstream CTR results

Deliverable 3 — validation report

• Aggregate computed liability vs MHCLG administrative total (~£40bn England)
• Per-LA comparison against total_council_tax_net
• Band distribution vs VOA dwelling counts
• Distributional validation (decile incidence) against an external benchmark
• Write up as a published validation note

Deliverable 4 — policy examples

• Band revaluation scenario
• Proportional property tax / council tax replacement
• Single-person discount reform
• Band D rate change by LA

Reference data

• MHCLG council tax levels 2026-27: https://www.gov.uk/government/statistics/council-tax-levels-set-by-local-authorities-in-england-2026-to-2027
• MHCLG council tax statistics collection: https://www.gov.uk/government/collections/council-tax-statistics
• Statutory band proportions: Local Government Finance Act 1992 s.5

Notes

Band amounts in MHCLG Table 9 are area figures — they include county, police, fire and parish precepts, not just the billing authority's own requirement. Any comparison against a billing-authority-only total needs to account for that.

Start by reading variables/input/consumption/property/council_tax.py, datasets/enhanced_cps.py, and the existing la_council_tax.csv and calibration-target files. This is a multi-deliverable tracker, so first agree on one unchecked work item; done requires that item, its validation, and the relevant model or data integration to be completed.