Treasury faces around £380m upfront cost on £2m+ mansion tax before April 2028 levy generates income

Treasury analysis reported on 6 May puts the upfront cost of Labour's proposed £2m+ mansion tax at around £380m before the April 2028 levy raises a penny — £230m in forgone stamp duty and inheritance tax over three years plus £150m in valuation costs. The mechanism is buyer behaviour around the £2m threshold: Hamptons figures show listings at £1.8m–£2m up 6% since the Budget while listings at £2m–£2.2m have fallen 7%. For sellers in the £2m+ band the levy is already shaping pricing decisions; for buyers, offers are being structured to stay below the cap. Treasury still projects £930m net by 2031, though agents warn the £2m threshold may drift down under future governments.