Give both OBR placements of Northern Ireland domestic rates in the fiscal partition

changelog.d/2662.changed.md

@@ -0,0 +1 @@
+Documented that the OBR shows Northern Ireland domestic rates in two places, a council tax line that appears to be the district rates and an other taxes line that appears to be the regional rate, while `domestic_rates` charges both.

policyengine_uk/data/fiscal_partition.yaml

@@ -88,6 +88,20 @@ sources:
     a forecast of Northern Irish domestic rates to Great Britain's, and are
     net of discounts and reduction schemes. Read 2026-10-11 from
     https://obr.uk/forecasts-in-depth/tax-by-tax-spend-by-spend/council-tax/
+  ni_domestic_rates: >-
+    OBR, Economic and fiscal outlook, March 2026, detailed forecast tables:
+    expenditure Table 4.1 ("Council tax receipts"), which its footnote calls
+    a breakdown of Table A.5's council tax line, and receipts Table 3.2
+    ("Other taxes"), which its footnote calls consistent with Table A.5's
+    other taxes line. ONS, Country and regional public sector finances,
+    financial year ending 2025, Northern Ireland revenue rows "Northern
+    Ireland Regional Domestic Rates" and "Northern Ireland District Domestic
+    Rates". Land & Property Services, "Rates paid by District Council and
+    Sector", domestic rates paid. Cells read 2026-10-25. Published at
+    https://obr.uk/efo/economic-and-fiscal-outlook-march-2026/,
+    https://www.ons.gov.uk/economy/governmentpublicsectorandtaxes/publicsectorfinance/datasets/countryandregionalpublicsectorfinancesrevenuetables
+    and
+    https://www.data.gov.uk/dataset/30535a44-0a05-4bff-98cf-001301a6b4d6/rates-paid-by-district-council-and-sector
   student_loans: >-
     Student loan repayments are not a row of Table A.5. In the March 2026
     EFO only the interest accrued on the loans enters receipts, in "Interest
@@ -447,8 +461,39 @@ tax_heads:
     obr_line: Council tax
     obr_table_3_1: null
     obr_line_note: >-
-      The OBR adds Northern Irish domestic rates to its council tax receipts
-      (see sources).
+      The head is the whole Northern Ireland domestic bill, the regional rate
+      and the council's district rate together. Land & Property Services
+      (LPS) reports £889.5m of domestic rates paid across NI in 2024-25. The
+      OBR shows NI domestic rates in two places and labels neither as
+      regional or district (see sources): "NI domestic rates" in its council
+      tax receipts, a flat £0.494bn in every year from the 2024-25 outturn to
+      2030-31 (expenditure Table 4.1), which appears to be the district
+      rates; and "Northern Ireland domestic rates" under other taxes, £485.3m
+      in 2024-25 (receipts Table 3.2), which appears to cover the regional
+      rate only. The Office for National Statistics (ONS) records NI
+      regional domestic rates (central government, £498m in 2024-25) and
+      district domestic rates (local government, with council tax, £441m)
+      separately. The reading rests on where each line
+      sits, not on its size: £0.494bn is nearer ONS's regional row than its
+      district row, and the two lines together (£0.979bn in 2024-25) exceed
+      both LPS's figure and ONS's two rows (£0.939bn). The head keeps the
+      Council tax row, where the OBR says its forecast adds NI domestic
+      rates. In the 2024-25 outturn that row (March 2026 Table A.5,
+      £47.417bn) is £0.273bn below Table 4.1's total (£47.690bn), so whether
+      it then includes NI domestic rates is not established; the two agree
+      in the forecast years. If the regional and district reading holds, the
+      head's scope is the two lines together, not either alone. obr_table_3_1 is null because Table
+      3.1's footnotes do not place NI domestic rates and the head appears to
+      span two Table A.5 rows. The
+      comment on gov.economic_assumptions.yoy_growth.finance_ni.domestic_rates
+      gives the evidence for the reading.
+    data_note: >-
+      On the certified dataset (policyengine-uk-data 1.58.1) the head totals
+      £0.52bn in 2024, the Family Resources Survey 2024-25 year, against
+      £0.89bn of LPS domestic
+      rates paid in 2024-25. policyengine-uk-data issue 520 tracks the level
+      and the data build's obr/domestic_rates target, which it reads from the
+      Table 4.1 line alone. Measured 2026-10-25.
     report_group: local_taxes
     payer: household
     totals: [gov_tax, household_tax, pre_budget_change_household_tax]

policyengine_uk/parameters/gov/economic_assumptions/yoy_growth.yaml

@@ -1520,7 +1520,8 @@ finance_ni:
     # 2019-20, the first year not published). It is a national average: it
     # does not reproduce any one council's bill or changes in reliefs.
     #
-    # Neither OBR March 2026 line covers the whole bill, and OBR labels
+    # Neither OBR March 2026 line is large enough to cover the whole bill
+    # (each is about half of LPS's £889.5m paid in 2024-25), and OBR labels
     # neither as regional or district; the attribution here is inferred.
     # Expenditure Table 4.1 holds "NI domestic rates" at £0.494bn in every
     # year to 2030-31 inside its council tax total, and ONS classes district
@@ -1529,9 +1530,11 @@ finance_ni:
     # taxes") appears to be the regional rate: ONS classes the regional
     # domestic rate as a central government tax, and with Table 3.2's NI
     # business rates line it sums to £0.914bn in 2026-27, against DoF's
-    # "just over £900million" from the regional rate that year. Receipts
-    # growth is not bill growth either: Table 3.2 grows 2.0% in 2026-27, a
-    # year whose domestic regional rate rose 5.0%.
+    # "just over £900million" from the regional rate that year. The reading
+    # rests on where the lines sit, not on their size: the £0.494bn line is
+    # nearer ONS's 2024-25 regional domestic row (£498m) than its district
+    # row (£441m). Receipts growth is not bill growth either: Table 3.2
+    # grows 2.0% in 2026-27, a year whose domestic regional rate rose 5.0%.
     values:
       # Outturn: published poundages. Regional rate 0.4574p in 2019-20 to
       # 2022-23, then 0.4848p, 0.5042p, 0.5294p and 0.5559p (2026-27). The