feat: add Scottish Budget 2026-27 tax and benefit changes

changelog_entry.yaml

@@ -0,0 +1,6 @@
+- bump: minor
+  changes:
+    added:
+      - Scottish Budget 2026-27 income tax threshold uplift (7.4% increase to basic and intermediate rate thresholds)
+      - Scottish Budget 2026-27 SCP Premium for under-ones (£40/week for children under 1)
+      - New parameter premium_under_one_amount for SCP Premium rate

policyengine_uk/parameters/gov/hmrc/income_tax/rates/scotland/rates.yaml

@@ -19,6 +19,9 @@ brackets:
         2023-04-06: 2_162
         2024-04-06: 2_306
         2025-04-06: 2_827
+        # Scottish Budget 2026-27: Basic rate threshold £16,537 total
+        # (above £12,570 PA = £3,967). 7.4% increase.
+        2026-04-06: 3_967
       metadata:
         uprating: gov.economic_assumptions.indices.obr.consumer_price_index
     rate:
@@ -32,6 +35,9 @@ brackets:
         2023-04-06: 13_118
         2024-04-06: 13_991
         2025-04-06: 14_921
+        # Scottish Budget 2026-27: Intermediate rate threshold £29,526 total
+        # (above £12,570 PA = £16,956). 7.4% increase.
+        2026-04-06: 16_956
       metadata:
         uprating: gov.economic_assumptions.indices.obr.consumer_price_index
     rate:
@@ -81,3 +87,5 @@ metadata:
   reference:
     - title: GOV.UK
       href: https://www.gov.uk/government/publications/rates-and-allowances-income-tax/income-tax-rates-and-allowances-current-and-past
+    - title: Scottish Budget 2026-27 - Income Tax Technical Factsheet
+      href: https://www.gov.scot/publications/scottish-income-tax-technical-factsheet/

policyengine_uk/parameters/gov/social_security_scotland/scottish_child_payment/amount.yaml

@@ -6,6 +6,7 @@ values:
   2022-11-14: 25
   2024-04-01: 26.70
   2025-04-01: 27.15
+  2026-04-01: 28.20
 metadata:
   unit: currency-GBP
   period: week

policyengine_uk/parameters/gov/social_security_scotland/scottish_child_payment/premium_under_one_amount.yaml

@@ -0,0 +1,18 @@
+description: Weekly amount of Scottish Child Payment Premium for children under 1.
+values:
+  # No premium before 2027-28
+  0001-01-01: 0
+  # Scottish Budget 2026-27 announced this for 2027-28
+  # Source: "will be paid in 2027-28"
+  # https://www.gov.scot/publications/scottish-budget-2026-2027/pages/6/
+  # This is a TOTAL amount, not a bonus on top of standard SCP
+  2027-04-06: 40
+metadata:
+  unit: currency-GBP
+  period: week
+  label: Scottish Child Payment Premium for under-ones weekly amount
+  reference:
+    - title: Scottish Budget 2026-27 - Finance Secretary's Statement
+      href: https://www.gov.scot/publications/scottish-budget-2026-2027/
+    - title: Scottish Government announcement
+      href: https://www.gov.scot/news/income-tax-proposals-for-2026-27-3/

policyengine_uk/reforms/reforms.py

@@ -4,7 +4,6 @@
     disable_simulated_benefits,
 )
 from .policyengine.adjust_budgets import adjust_budgets
-from .scotland import create_scottish_child_payment_reform
 from policyengine_core.model_api import *
 from policyengine_core import periods
 
@@ -16,7 +15,6 @@ def create_structural_reforms_from_parameters(parameters, period):
         create_household_based_hitc_reform(parameters, period),
         disable_simulated_benefits(parameters, period),
         adjust_budgets(parameters, period),
-        create_scottish_child_payment_reform(parameters, period),
     ]
     reforms = tuple(filter(lambda x: x is not None, reforms))