Knight Frank has issued a pointed warning to owners of Britain's most expensive homes: the High Value Council Tax Surcharge unveiled in last autumn's Budget, due to take effect in 2028, should be treated as a floor rather than a ceiling. The levy, which will impose annual charges of between £2,500 and £7,400 on properties worth £2 million or more, was framed by the Treasury as a modest and targeted revenue-raiser. But the agency's analysis suggests that once the mechanism is in place, successive chancellors will find it politically far easier to raise the rates or lower the threshold than to introduce a wholly new wealth tax from scratch.