Households without a BRMA get Maidstone's Local Housing Allowance in every region #2256

What's wrong

brma (Broad Rental Market Area) is an input with no formula and a default of MAIDSTONE. The Local Housing Allowance cap reads it directly. Any household without a BRMA therefore gets Maidstone's LHA rates, whatever its region: London, Scotland, Wales and Northern Ireland included.

In a household calculation that sets only the region, a private renter's Universal Credit housing element is capped at Maidstone's rates. The public UK transfer dataset (enhanced_cps_2025.h5) stores no BRMA either. On main e89b8abc, all 28,532 of its households compute as Maidstone in every region.

In the PolicyBench UK audit, 43 of 100 sampled households rent privately. The independent judge found the award undetermined for those whose rent is near the cap. For example, the two-bedroom LHA is £450 a month in West Pennine and £875 in Central Greater Manchester, both in the North West.

Suggested fix

Give brma a formula for when none is supplied. It should pick an area inside the household's region, either a fixed representative area per region or a draw weighted by the region's renters, rather than Maidstone everywhere. Which area represents a region is a modelling choice.

PolicyBench now states a fixed BRMA per region in its prompt and supplies it, so its references no longer depend on this default.