Only 4,000 people will pay the new £30,000 annual charge on wealthy UK-based foreigners that takes effect next year, official Treasury estimates show.

The revelation of the small number of non-doms that will be hit by Alistair Darling's pre-Budget report move comes as the opposition Conservatives launch a new counter-attack against the government over the issue. George Osborne, the shadow chancellor, told the Financial Times on Sunday that documents obtained under the Freedom of Information Act meant Mr Darling "has got some explaining to do".