Owners of Britain's most expensive homes are facing the prospect of losing up to £500,000 in property value amid growing speculation that the Treasury is preparing a new tax targeting high-value residential real estate. Reports suggest that properties worth £2 million or more could be hit with an annual charge or a revamped capital gains regime designed to capture wealth locked up in bricks and mortar, a move that estate agents warn is already causing a chilling effect on transactions in the prime market. For an industry still recalibrating after successive stamp duty surcharges and mortgage rate volatility, this latest intervention threatens to reshape the top end of the market just as it was showing tentative signs of stabilising.