Use published LHA determinations and apply Sch 3B paras 3 and 3A

.gitignore

@@ -55,6 +55,7 @@ policyengine_uk/calibration/*.h5
 *.ipynb
 !docs/**/*.ipynb
 !uprating_growth_factors.csv
+!policyengine_uk/parameters/gov/dwp/LHA/lha_published_rates_sources.csv
 
 # Virtual environments
 .venv/

changelog.d/2012.fixed.md

@@ -0,0 +1 @@
+- Local Housing Allowance rates now come from the published determinations instead of the 30th percentile of the 2020 list of rents uprated by the private rent index. Sources: VOA, the Welsh and Scottish Governments, the NIHE, and monthly Universal Credit rates from DWP (Great Britain) and nidirect (Northern Ireland). Determinations from April 2020 are recomputed from the published 30th percentile rents with the national maxima, the anomalous-rate rule (Rent Officers Order Sch 3B para 3) and the March 2020 minimum (para 3A, which also applies to Northern Ireland's Universal Credit rates). This reproduces every published rate and stops rates falling with dwelling size. Universal Credit uses the monthly determination rather than 52 weeks of the weekly one.

changelog.d/2036.fixed.md

@@ -0,0 +1 @@
+- Replaced the Scottish lists of rents, which were copies of English BRMAs' lists, with Rent Service Scotland's own lists released under FOI 202200303624, so percentile reforms scale Scottish LHA rates by Scotland's rent distributions.

docs/book/programs/gov/dwp/housing-benefit.ipynb

@@ -47,6 +47,30 @@
     "The take-up gate (`would_claim_housing_benefit`) is applied inside `housing_benefit_pre_benefit_cap`."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "lha0rates0published0determinations",
+   "metadata": {},
+   "source": [
+    "## Local Housing Allowance rates\n",
+    "\n",
+    "A private renter's eligible rent is capped at the Local Housing Allowance (LHA) for their Broad Rental Market Area (BRMA) and LHA category: shared accommodation, or one to four bedrooms (`LHA_category`). Rent officers determine the rates each January for the year from April. In England this is the Valuation Office Agency, in Wales Rent Officers Wales, in Scotland Rent Service Scotland, and in Northern Ireland the Northern Ireland Housing Executive.\n",
+    "\n",
+    "PolicyEngine reads the published determinations from `parameters/gov/dwp/LHA/lha_published_rates.csv.gz`. `scripts/build_lha_published_rates.py` builds that table from the source files listed, with their hashes, in `lha_published_rates_sources.csv`. For each determination from April 2020, the rate is recomputed from the published 30th percentile rents, following [Schedule 3B](https://www.legislation.gov.uk/uksi/1997/1984/schedule/3B) to the Rent Officers (Housing Benefit Functions) Order 1997:\n",
+    "\n",
+    "1. the lower of the percentile rent and the national maximum (`gov.dwp.LHA.maximum`), paragraph 2(2), rounded to the nearest penny (paragraph 2(10));\n",
+    "2. raised to the rate of any smaller category, paragraph 3;\n",
+    "3. for determinations from April 2024, no lower than the rate determined on 31 March 2020 (`gov.dwp.LHA.march_2020_minimum`), paragraph 3A.\n",
+    "\n",
+    "While `gov.dwp.LHA.freeze` is true, the rates of the last unfrozen year apply (the Modification Orders for 2021 to 2023, 2025 and 2026). A year is the fiscal year from April, so 2025 means April 2025 to March 2026. These rules reproduce every published rate since April 2020. Where a publisher gives no separate percentile for a reset year (Wales and Northern Ireland in April 2020, Northern Ireland in April 2024), the published rate stands in for it, so for those cells the match shows only that the rules leave an unadjusted rate alone. Universal Credit has its own monthly determination ([Schedule 1](https://www.legislation.gov.uk/uksi/2013/382/schedule/1) to the Universal Credit Functions Order 2013), with monthly maxima (`gov.dwp.LHA.maximum_monthly`). Its monthly tables come from DWP for Great Britain and from nidirect for Northern Ireland from April 2024; Northern Ireland's earlier monthly rates were not published, so the model converts the weekly percentile (365/7 weeks a year over 12 months). Rent Officers Wales's April 2022 and 2023 tables restate 14 of the weekly April 2020 rates they say they hold, and DWP's monthly tables restate the same 14 plus three more by a penny or two. Each restated figure is a round rent (16 of the 17 monthly figures are multiples of £5; the other, Vale of Glamorgan one-bedroom at £434.52, is £100 a week), which reads as a correction, so the model takes them as published: a held year adjusts the held determination's percentile rent (so a reform to the maximum still binds), and the March 2020 minimum uses the restated figures. Determinations before April 2020 are used as published, because the model does not encode the rules of that period: CPI and 1% uprating, then the 2016 to 2020 freeze with targeted affordability uplifts.\n",
+    "\n",
+    "Reforms work as follows:\n",
+    "\n",
+    "- Lifting a freeze uses the percentile rents published for that year where they exist. The VOA, Rent Officers Wales and the Scottish Government publish them even for frozen years. The NIHE has not since 2018, so Northern Ireland, and the few Welsh cells missing from a table, use the latest earlier percentile grown with `gov.indices.private_rent_index`.\n",
+    "- Beyond the latest table, the latest percentile rent grows with `gov.indices.private_rent_index`.\n",
+    "- A percentile other than the 30th (`gov.dwp.LHA.percentile`) scales the published one by the ratio of the two percentiles in the model's list of rents for the same BRMA and category. The English lists are the VOA's and the Scottish lists are Rent Service Scotland's own. The Welsh and Northern Irish lists in the file are copies of English ones, so those BRMAs take the median English ratio for the category.\n"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "8dd0d8092fe74a7c96281538738b07e2",

policyengine_uk/parameters/gov/dwp/LHA/README.md

@@ -1 +1,9 @@
 # Local Housing Allowance
+
+## Lists of rents
+
+`lha_list_of_rents.csv.gz` holds one row per rent in the lists behind the April 2019 and April 2020 determinations (`year`), with its BRMA and LHA category. The model uses it only to turn the published 30th percentile into another percentile when a reform changes `percentile`.
+
+- **England:** the Valuation Office Agency's published lists.
+- **Scotland:** Rent Service Scotland's records, released by the Scottish Government under FOI 202200303624. The list for April Y is the sheet for the year to September Y-1. `scripts/build_scottish_list_of_rents.py` rebuilds these rows from the pinned workbook. In 522 of 540 cells (April 2017-2022), those sheets reproduce the published 30th percentiles to the penny.
+- **Wales and Northern Ireland:** copies of English BRMAs' lists, each matched on the nation's April 2019 rate (issue #2036). Their percentile reforms use the median English ratio for the category instead.

policyengine_uk/parameters/gov/dwp/LHA/__init__.py

@@ -1,4 +1,10 @@
 import pandas as pd
 from pathlib import Path
 
-lha_list_of_rents = pd.read_csv(Path(__file__).parent / "lha_list_of_rents.csv.gz")
+
+def __getattr__(name):
+    # The list of rents is large, and only percentile reforms need it, so it
+    # is read on first access rather than when the package is imported.
+    if name == "lha_list_of_rents":
+        return pd.read_csv(Path(__file__).parent / "lha_list_of_rents.csv.gz")
+    raise AttributeError(name)

policyengine_uk/parameters/gov/dwp/LHA/freeze.yaml

@@ -1,5 +1,5 @@
 description: >-
-  While this parameter is true, LHA rates are frozen in cash terms at the level set in the most recent year in which it was false. When this parameter is false, values are set at the (default 30th) BRMA percentile of that year's rents. Values from 2027 onward reflect announced rather than enacted policy: no Modification Order has been made beyond 2026-27, and the Autumn Statement 2023 costing maintains the April 2024 uplift in cash terms thereafter.
+  While this parameter is true, LHA rates are frozen in cash terms at the level determined in the most recent year in which it was false. When it is false, rates are determined from that year's percentile rents (the 30th percentile by default), the national maximum, the anomalous-rate rule and, from April 2024, the March 2020 minimum. A year here is the fiscal year from April, so the value from 6 April 2025 governs the rates in force from April 2025. Determinations before April 2020 are taken as published, since they followed CPI and 1% uprating and then the 2016 to 2020 freeze with targeted affordability uplifts, so this parameter governs determinations from April 2020 onward. Values from 2027 onward reflect announced rather than enacted policy: no Modification Order has been made beyond 2026-27, and the Autumn Statement 2023 costing maintains the April 2024 uplift in cash terms thereafter.
 values:
   2015-01-01: false
   2020-04-06:
@@ -8,6 +8,8 @@ values:
       reference:
         - title: The Social Security (Coronavirus) (Further Measures) Regulations 2020, reg. 4 (April 2020 reset to the 30th percentile)
           href: https://www.legislation.gov.uk/uksi/2020/371/regulation/4/made
+        - title: The Social Security (Coronavirus) (Further Measures) Regulations (Northern Ireland) 2020, reg. 4
+          href: https://www.legislation.gov.uk/nisr/2020/53/regulation/4/made
   2021-04-06:
     value: true
     metadata:
@@ -18,12 +20,20 @@ values:
           href: https://www.legislation.gov.uk/uksi/2021/1380/made
         - title: The Rent Officers (Housing Benefit and Universal Credit Functions) (Modification) Order 2023 (determinations in 2023)
           href: https://www.legislation.gov.uk/uksi/2023/6/made
+        - title: The Housing Benefit and Universal Credit Housing Costs (Executive Determinations) (Modification) Regulations (Northern Ireland) 2021
+          href: https://www.legislation.gov.uk/nisr/2021/14/made
+        - title: The Housing Benefit and Universal Credit Housing Costs (Executive Determinations) (Amendment and Modification) Regulations (Northern Ireland) 2022
+          href: https://www.legislation.gov.uk/nisr/2022/15/made
+        - title: The Housing Benefit and Universal Credit Housing Costs (Executive Determinations) (Modification) Regulations (Northern Ireland) 2023
+          href: https://www.legislation.gov.uk/nisr/2023/4/made
   2024-04-06:
     value: false
     metadata:
       reference:
         - title: The Rent Officers (Housing Benefit and Universal Credit Functions) (Amendment) Order 2024 (April 2024 reset to the 30th percentile)
           href: https://www.legislation.gov.uk/uksi/2024/11/made
+        - title: The Housing Benefit and Universal Credit Housing Costs (Executive Determinations) (Amendment) Regulations (Northern Ireland) 2024
+          href: https://www.legislation.gov.uk/nisr/2024/3/made
   2025-04-06:
     value: true
     metadata:
@@ -32,6 +42,10 @@ values:
           href: https://www.legislation.gov.uk/uksi/2025/5/made
         - title: The Rent Officers (Housing Benefit and Universal Credit Functions) (Modification) Order 2026
           href: https://www.legislation.gov.uk/uksi/2026/5/made
+        - title: The Housing Benefit and Universal Credit Housing Costs (Executive Determinations) (Modification) Regulations (Northern Ireland) 2025
+          href: https://www.legislation.gov.uk/nisr/2025/1/made
+        - title: The Housing Benefit and Universal Credit Housing Costs (Executive Determinations) (Modification) Regulations (Northern Ireland) 2026
+          href: https://www.legislation.gov.uk/nisr/2026/2/made
         - title: Autumn Statement 2023 policy costings (April 2024 uplift maintained in cash terms thereafter)
           href: https://assets.publishing.service.gov.uk/media/655d0a83544aea000dfb321d/Autumn_Statement_2023_Policy_Costings_-_Final.pdf#page=16
 metadata: