housing/total_mortgage cites the ONS rent bulletin, which carries no mortgage figure

What

policyengine_uk_data/targets/sources/housing.py builds the national calibration target housing/total_mortgage as £1,100/month × 12 × 7.5m owner-occupiers with a mortgage (~£99bn), with reference_url pointing at the ONS bulletin "Private rent and house prices, UK: March 2026":

https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/privaterentandhousepricesuk/march2026

That bulletin publishes PIPR average private rents (UK £1,374/month at February 2026, etc.) and house-price statistics. It carries no average mortgage payment figure at all — the citation does not support the value. The module docstring lists sources for rent and tenure counts but names no source for the £1,100, and the 7.5m mortgagor-household count is likewise an unpinned ~ approximation with no published table behind it.

How this was found

During the uk-data → Chronicle migration (chronicle#133, chronicle#159), porting housing/total_mortgage was refused because no publisher source exists for the value; it is recorded as a first-class blocked row in chronicle's docs/pe-uk-source-checklist.md. Review on that PR flagged that the mis-citation is live in this repo and deserves its own issue rather than living only in a PR body.

Nearest sourced anchor (not a drop-in replacement)

English Housing Survey 2023-24 rented sectors, Annex Table 1.7: mean weekly housing costs for all mortgagors = £222.42/week ≈ £964/month. Caveats: England only (not UK), and per the table's note 5, EHS mortgagor costs include households set to a nominal £0.02/week (shared owners with no outstanding loan, equity-release mortgages at 55+), which depresses the mean. So it anchors the order of magnitude but cannot simply be substituted.

Ask

Rebuild housing/total_mortgage on a real published source — both the per-household payment and the mortgagor-household count need pinned publisher tables — or retire/replace the target. Until then the target inherits a citation that does not support it.

Start in policyengine_uk_data/targets/sources/housing.py and review chronicle/docs/pe-uk-source-checklist.md, especially the blocked housing/total_mortgage row. Verify publisher tables for both the per-household mortgage payment and mortgagor-household count, then document sourced values or retire/replace the target if no suitable source exists.