Scottish LBTT Additional Dwelling Supplement stale at 6% (should be 8% from 5 December 2024)

Summary

PolicyEngine-UK's Scottish LBTT Additional Dwelling Supplement (ADS) parameter is stale. It is set to 6%, but the ADS rate has been 8% for transactions on or after 5 December 2024.

Current value in PolicyEngine-UK 2.89.2

gov.revenue_scotland.lbtt.residential.additional_residence_surcharge:

2016-04-01: 0.03
2019-01-25: 0.04
2022-12-16: 0.06   # latest — no 2024 entry

So lbtt_on_residential_property_transactions applies a 6% surcharge to additional-dwelling purchases, understating the charge for any second-home transaction from 5 December 2024 onward.

Correct value

The ADS rate increased from 6% to 8% for contracts entered into on or after 5 December 2024 (Scottish Budget 2025-26), implemented under the Land and Buildings Transaction Tax (Scotland) Act 2013 Schedule 2A.

Source: Revenue Scotland — Additional Dwelling Supplement (https://revenue.scot/taxes/land-buildings-transaction-tax/additional-dwelling-supplement-ads): "For transactions on or after 5 December 2024 the ADS is 8% of the purchase price."

Suggested fix

Add 2024-12-05: 0.08 to additional_residence_surcharge.yaml with the Revenue Scotland reference.

Start with additional_residence_surcharge.yaml and review the existing dated rates and Revenue Scotland reference given in the issue. Add the 5 December 2024 rate and reference, then run the relevant parameter or policy tests to confirm that transactions from that date use the updated surcharge.