Values in some of the capital's priciest postcodes have dropped by close to £300,000 in a year. For HNW brokers, the number that matters isn't the fall in list price itself, it's whether clients' sums insured have kept pace with reality on either side of it.
London remains the only English region where house prices are falling year-on-year. The Office for National Statistics recorded a 2.5% annual decline to June 2026, taking the capital's average price to £554,000. That's the tenth consecutive month of annual falls, even as the rest of England posted growth of 1.8% and the UK overall rose 2%.
The regional average hides a much sharper correction at the top end. Westminster, covering Mayfair, Belgravia and St John's Wood, saw its average price fall 25.4% year-on-year to £854,000, a drop of £291,000. Kensington and Chelsea, still England's most expensive borough at £1.25 million, fell 14.7%. Hammersmith and Fulham dropped 13.3% to £726,000, and Camden fell 7.1% to £833,000.
Buildings sums insured are meant to track what it would cost to reconstruct a property, not what it would sell for. In prime London right now, those two figures are pulling apart rather than moving together.
A Belgravia townhouse that has lost several hundred thousand pounds in resale value hasn't necessarily lost anything in reconstruction terms. Listed status, bespoke joinery, imported stone and a shortage of heritage-trained contractors keep pushing rebuild costs up regardless of what sale prices are doing. The ABI/BCIS House Rebuilding Cost Index, the benchmark insurers and surveyors use to set reinstatement values, showed domestic rebuilding costs up 3.9% in the year to July 2026. BCIS has warned separately that the gap this creates between rebuild cost and sums insured is a live exposure rather than a theoretical one.
The underlying figures back that up. Research from the Chartered Insurance Institute puts the average UK property's cover at only around two-thirds of what a full rebuild would cost, with roughly seven in ten properties underinsured to some degree. Insurance Business UK has reported BCIS warnings that rebuild costs are outpacing sums insured as drought-linked subsidence claims expose valuations that haven't been reviewed in years, and that rebuild cost inflation has climbed to 4.9% as oil price shocks push up materials and haulage costs. A Mayfair flat selling for less than it did last summer doesn't touch any of that.
There's a risk running the other way too. A homeowner who sees their local paper-value fall might reasonably decide their buildings cover is now too generous and ask a broker to trim it. That's exactly the wrong call if the sum insured was set against rebuild cost rather than sale price in the first place. Pointing clients to a proper reinstatement cost assessment, rather than the latest Rightmove estimate, is the safer conversation to have.
There's a separate reason for HNW clients to have their property valuations looked at again. The High Value Council Tax Surcharge, the so-called "mansion tax," is already legislated to take effect from April 2028, based on 2026 valuations, for English homes worth £2 million or more. Prime Minister Andy Burnham, who took office in July 2026, has been reported to be weighing whether to lower that threshold to £1.5 million, which would pull tens of thousands more properties into scope.
The valuation exercise HMRC's Valuation Office Agency runs for the surcharge is a different process from a RICS reinstatement cost assessment done for insurance purposes, and the two figures won't match. But a client having their property freshly valued for tax reasons is a reasonable prompt for a broker to check whether the insurance-side figure still holds up too, especially for anyone who hasn't had a full rebuild assessment in the past three to five years.
Higher mortgage rates in the wake of the Iran war, combined with London's comparatively steep stamp duty bills, are the most commonly cited drags on demand at the top of the market. An economist at PwC has argued the underperformance runs deeper than financing costs alone, pointing to high starting valuations, elevated transaction costs and prime London's particular exposure to swings in overseas buyer demand.
Some forecasters see the falls easing rather than continuing. Buying agency Garrington's chief executive, Jonathan Hopper, has pointed to recent month-on-month growth in London values as a possible sign the market is close to bottoming out, with buyers who had been waiting on the sidelines starting to return. Knight Frank's head of UK residential research, Tom Bill, is more cautious, expecting prices to stay broadly flat for the rest of the year as inflation and pre-Budget speculation continue to weigh on sentiment.
The practical message for HNW brokers is that insurance doesn't necessarily move with the market. A client's sale price, asking price or council tax valuation is not a reliable stand-in for rebuild cost, and a fast-moving market makes it easier for the gap between the two to widen without anyone noticing. It's also a reasonable opening to talk to affluent clients about risk beyond bricks and mortar: growing cyber exposure among high-net-worth households, for one, or the way underwriters are increasingly factoring social media activity into HNW risk assessment.
Standard policies can't handle this complexity, which is why specialist products exist. BIBA's high-value home scheme with iprism is one example, and insurers keep investing in the space: NFU Mutual recently strengthened its high-net-worth team with a senior hire. Claims specialists have also flagged how much more complicated high-end properties get when something does go wrong, with smart home systems and contemporary collectibles adding new layers to settling HNW claims.
SW1 and SW7 losing a quarter of their value in a year is a striking headline. For a broker, the more useful question is whether the figure on the client's policy schedule was ever really about the sale price at all.
