Flood and subsidence exposure is creating hidden portfolio losses that macro models are dramatically underestimating
Mortgage lenders are sitting on collateral risk far larger than their current models suggest, according to new research that found climate-related hazards are already depressing UK property values at a pace regulators and risk teams have yet to fully account for.
A Winter 2026 study by PriceHubble and MIAC Analytics combined hyper-local property data with Twinn climate risk scores and portfolio stress-testing to reveal a gap between macro-level risk assumptions and what is actually playing out at the postcode level.
The findings carry direct implications for brokers advising on flood- and subsidence-exposed properties, and for lenders managing residential mortgage books.
Flood discounts are already baked in
Properties at the highest flood risk traded at an average 2.1% discount to local market prices in Q3 and Q4 2024, the study found. Terraced houses recorded the steepest haircut at 3.8%, while lower-value markets showed a 2.7% gap. Zooming in further, analysis of 282,000 transactions showed high-risk properties trading at an average 6% discount to the lowest-risk properties within the same region.
Yorkshire and the Humber, the East Midlands, and the east of England were the most exposed areas. In Hull, 91% of all 2024 property transactions involved homes rated at high flood risk.
Mark Cunningham, managing director of PriceHubble UK, warned broad regional data is masking the true scale of the problem.
"Regional data can make you complacent. It's at the local authority or postcode level that you see the true risk picture," he said.
The discount is only part of the exposure. More than half of all highest-risk flood properties sold in 2024 had rebuild costs that exceeded their sale price. In the lowest-value price quartile, rebuild costs ran 56% above market value on average – a dynamic that raises serious underinsurance and solvency concerns for households and, by extension, for the lenders secured against those assets.
Those concerns are already beginning to surface in mortgage markets. Modelling by Bank Underground suggests the share of UK mortgagors without insurance could rise from around 5% today to between 7% and 10% by 2050 – and as high as 16% following a severe flood event. Brokers and lenders are already reporting closer scrutiny on flood-exposed properties, with some borrowers facing delays and tighter underwriting conditions where cover is harder to obtain.
Subsidence: the slower-burning threat
Flood risk may dominate headlines, but subsidence presents a parallel and accelerating challenge. Currently 4% of UK homes sit in the two highest subsidence risk bands. Under medium emissions scenarios, that share is projected to reach 21% by the 2050s, according to the Association of British Insurers (ABI). Castle Point in Essex recorded the sharpest local concentration, with 82% of 2024 transactions falling in the highest subsidence risk category.
Claims data confirms the pressure is already building. The ABI recorded £153 million in subsidence-related home insurance claims in H1 2025 alone, with almost 9,000 households supported at an average payout of £17,264 per claim.
Stress tests reveal the scale of the gap
The study's most striking findings came from portfolio stress-testing. MIAC Analytics modelled a £330 million lifetime mortgage portfolio backed by 5,000 UK residential properties. Under a no-additional-action climate scenario, applying property-level risk data produced losses nearly seven times higher than the base case.
In London, property-specific risk data reduced projected values by 30.9% against the macro baseline. Across all regions, the average reduction reached 21.6%.
Those projections sit against a market already under strain. UK property insurance claims hit a record £6.1 billion in 2025. Domestic flood claims jumped 38% to £312 million and subsidence payouts reached an all-time high of £307 million, according to the ABI. Deloitte has forecast that home insurers will swing to a net loss in 2026, with the combined ratio expected to reach 102.1%.
The Prudential Regulation Authority's (PRA) Dynamic General Insurance Stress Test, launched in May, is already pressing firms on exactly this kind of exposure. The study called for postcode and address-level risk analytics to become standard practice in lending, underwriting, and portfolio modelling.
The Flood Re safety net winds down in 2039. After that, pricing reverts to fully risk-reflective levels – and the properties that are hardest to insure today will become harder still to mortgage. For brokers, that is not a distant problem. It is the next valuation on their desk.
Want to be regularly updated with mortgage news and features? Get exclusive interviews, breaking news, and industry events in your inbox – subscribe to our FREE daily newsletter. You can also follow us on Facebook, X (formerly Twitter), and LinkedIn.
