Alistair Darling appeared last night to be bowing to growing pressure to rethink his plan to increase taxation on non-domiciled foreigners living in Britain.

The Treasury is understood to be looking at possible concessions after a wave of protests raised fears of an exodus of wealth-creating foreigners from the City.

Officials were examining the detail of the proposals and looking at ways of “making clarifications”.

The Times understands they are considering introducing provisions to assure non-doms that the Treasury’s aim was not to pry into their world-wide tax affairs, but only to tax the earnings they bring to Britain.

The rethink comes as business leaders renewed attacks on Mr Darling’s planned crackdown on non-doms.

Adrian Beecroft, chief investment officer of Apax Partners, one of Britain’s top private equity groups, said: “I just think it’s daft. There’s a whole lot of reasons why London has become the world’s financial centre and one of them is the treatment of non-doms.

"So what the hell is the point of trying to get a bit more tax revenue if you end up scaring them all away and putting a lot of people out of their jobs?”

Mr Beecroft said that he knew of several private equity executives who were planning to move to Switzerland to avoid Mr Darling’s crackdown.

Chris Sanger, a partner in Ernst & Young and deputy chairman of the tax faculty of the Institute of Chartered Accountants, said: “Many of our clients have already started to put in place how they will leave the UK. There is very little time left for the Treasury to come out and signal a delay.”

Last night it emerged that Dermot Smurfit, the Irish entrepreneur who has lived in the UK as a non-dom for 20 years, is considering moving to Monte Carlo or Switzerland if the Treasury imposes the new charges.

Although the Conservatives were first to announce proposals to clamp down on non-doms last autumn, George Osborne, Shadow Chancellor, last night urged Mr Darling to drop his plans and to adopt the Tory idea of a £25,000 charge on non-doms.

Mr Osborne believes this will raise more than £3 billion, far more than the £650 million that Mr Darling has said he could raise from his plan.

Mr Osborne told the Chancellor: “It is not too late to abandon your ill-thought out and badly conceived plans.”

The Government’s plan is for a £30,000 charge that would be levied only if the nondoms had lived in Britain for seven years.

At greatest risk may be London’s maritime services industry, including the Baltic Exchange, which depends on a small but wealthy community of Greek shipowners.

These tycoons, who include the Niarchos, Onassis and Embiricos families, provide the financial backbone for London’s ship-broking market.

Jeremy Penn, the chief executive of the Baltic Exchange, said that tax was a key factor in making London the centre of the world shipping market.

He said: “The covenant that existed between the Government and the nondomiciled resident shipowners has been broken.”

Ian Harrison, a director at the London Investment Banking Association, said: “The proposed changes could make it much more difficult for our members to recruit and retain top-class people from around the world.”