Rachel Reeves's flagship reforms could destroy Britain's most successful investment product, a Treasury watchdog has warned. The host of new rules, including a new 22pc tax on the formerly tax-free Isa, put savers and investors at risk of “serious confusion”, according to Dame Meg Hillier MP, the Labour chairman of the Treasury select committee. In an exclusive interview with Telegraph Money, Dame Meg said: “I'm concerned this is breaking the Isa brand.