The Conservatives pledged Saturday to impose a US-style tax on banks to claw back money spent bailing them out, just weeks before a general election they are tipped to win.

"We had the biggest bank bail-out in the world. We can't just carry on as if nothing happened," said Conservative leader David Cameron, whose party is leading opinion polls ahead of the vote expected on May 6.

"In America, President (Barack) Obama has said he will get taxpayers back every cent they put in. Why should it be any different here?

"So I can announce today that a Conservative government will introduce a new bank levy to pay back taxpayers for the support they gave and to protect them in the future.

"No, it won't be popular in every part of the City (of London, the financial district). But I believe it's fair and it's necessary."

Obama unveiled his plan on January 14 for a new fee on major banking firms to recover "every single dime" taxpayers shelled out to rescue Wall Street from the economic crisis.

Conservative party sources said they would go ahead with the planned levy even if there was no international support, although it would be limited. "We would not impose a massive tax unilaterally," a source said.

However, financial services minister Paul Myners condemned the plan as "ill thought-out", saying: "This kind of tax on bankers needs to be international...

"The UK-only bank tax the Tories want is a sure-fire way of encouraging a banking exit from the UK -- raising costs to borrowers, damaging Britain's competitiveness and costing tens of thousands of jobs across the country."

Prime Minister Gordon Brown has long advocated some kind of globally co-ordinated levy on the banking sector, and the plan is expected to be included in his government's budget announcement on Wednesday.

The Financial Times reported Saturday that finance minister Alistair Darling will use his budget statement to give detailed backing to a bank levy, while stressing that it would only apply if there was international agreement.