Subsidence Risk by Postcode UK 2026: How to Check, What Postcodes Are Highest Risk, Insurance Impact

Shrink-swell clay subsidence is the most common cause of UK subsidence claims and concentrates in London, the South East, parts of East Anglia and the Midlands. Here's how to check the address you're buying for free, and how the £7.99 PostcodeCheck Buyer Report adds tree-proximity and insurance impact.

UK subsidence hotspots

The British Geological Survey (BGS) categorises every UK postcode by clay shrink-swell susceptibility. The five-band scale runs from Very Low (no measurable risk) to Very High (high probability of seasonal ground movement).

• Very High: London Clay belt (most of central + outer London), Essex, parts of Kent, Hertfordshire, Bedfordshire
• High: Greater London, North Kent, parts of East Anglia, Cambridgeshire, parts of Berkshire and Buckinghamshire
• Moderate: Outer South East, parts of the Midlands
• Low: North West, North East, Scotland, Wales, South West (mostly)

ABI data shows London + South East together account for 70%+ of UK subsidence claims by value. The pattern peaks after dry summers (2003, 2018, 2022) when clay shrinks rapidly.

What actually causes subsidence

1. Shrink-swell clay drying out — accounts for ~70% of UK claims. Mature trees within 10-15m exacerbate the effect by extracting groundwater.
2. Coal mining void collapse — see the coal mining check for those areas (Coal Authority typically funds remedial work).
3. Leaking drains and water mains — water erodes soil under foundations. Common in Victorian properties.
4. Salt mining / chalk solution features — Cheshire (Northwich, Middlewich), parts of Lincolnshire and Hertfordshire (chalk).
5. Embankment / made-up ground — properties on infilled valleys or old industrial sites.

How to check (free)

1. Go to BGS GeoIndex at bgs.ac.uk/data/services/geoindex.html
2. Search the postcode
3. Toggle the "Shrink-swell hazard" layer
4. Note the susceptibility band for the property

The free BGS map shows the geological hazard, not the address-level risk. A property in a Very High clay-shrink area without nearby trees and with stable foundations is lower risk than the same band with an oak tree 8m away.

What the £7.99 Buyer Report adds

• BGS shrink-swell clay band for the address
• Tree-proximity assessment (mature trees within 15m)
• Insurance impact summary — what to expect on quotes
• Plus flood, coal mining, radon, contaminated land, planning, crime trajectory + 6 other buyer risks
• One PDF, instant after payment

Subsidence-prone properties: red flags during viewing

• Diagonal cracks running from window or door corners (especially across multiple courses of brick)
• Cracks wider than a 1p coin
• Doors and windows that stick or won't close properly
• Bay window separating from the main building
• Mature trees within 15m of the building (especially oak, ash, willow, poplar — high-water-demand species)
• Recent extensions on the original footprint without obvious new foundations
• Fresh repointing or filler in suspicious patterns

Insurance impact

• Very Low / Low band, no claim history: standard premium, no flood-equivalent loading
• Moderate / High band, no claim history: £100-£300 per year more than the equivalent low-risk address
• Very High band, no claim history: £300-£600 more, larger excess on subsidence claims
• Active or recent (within 10 years) subsidence claim history: standard insurers usually refuse, specialist insurer at £1,000-£2,000+ per year, with subsidence excluded for some renewal cycles

Always ask the seller for the property's subsidence claim history. It's on the Land Registry record and on insurance Claims Underwriting Exchange (CUE), so you can verify with a written question to the seller and a Section 22 enquiry through your solicitor.