Britain's wealthiest people owe the taxman as much as £1.9billion, the National Audit Office has found in the wake of Theresa May's pledge to crackdown on tax avoidance.

The spending watchdog said that one in six of Britain's 6,500 wealthiest individuals have used tax avoidance schemes and admitted that HMRC has found investing whether they are paying the right amount "challenging".

However, it said that HMRC's "high net worth unit", a team of nearly of 400 officials focused on those earning more than £20million, managed to recoup an extra £416million last year.

The figure is twice as much as in 2011. It comes after Mrs May used her speech at the Conservative Party conference to warn wealthy people who fail to pay their taxes: "We're coming after you".