David Cameron has committed the Tories to imposing a new tax on banks as both main parties battled to convince voters they would claw back billions of pounds from the financial sector.
The Opposition leader said the US-style levy is needed to ensure taxpayers are repaid in full for the bail-out of financial institutions and protected from future collapses.
His firm pledge came amid renewed confidence of international backing for such a levy - although party sources indicated it would press ahead unilaterally with a more limited measure if not.
Chancellor Alistair Darling is expected to use next week's Budget to signal the Government's support for a global bank tax, although only as part of an international agreement.
He will set out detailed options in Wednesday's statement but will insist money raised should go into Treasury coffers and not be used for an insurance fund against future collapse, the Financial Times said. There are fears that the existence of an insurance fund could act to encourage risk-taking and that any unilateral action could prompt an exodus of banks from the City to less punitive regimes abroad.
The Conservatives have not yet given any detail of how their scheme would operate. US President Barack Obama has signalled his intent to impose a "responsibility fee" and Sweden has introduced a levy.
Mr Cameron singled out the banking industry as one example of "vested interests" he is determined to confront and who he accuses Prime Minister Gordon Brown of failing to stand up to.
"We had the biggest bank bail-out in the world. We can't just carry on as if nothing happened," he said. "In America, President 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. But I believe it's fair and it's necessary."
Mr Brown has been a leading advocate of some form of co-ordinated levy on the banks, which could bring in tens of billions of pounds a year from the financial services sector worldwide. He was forced to abandon his preferred option - a "Tobin" tax on transactions - but hopes the IMF will throw its weight behind a measure at its April meeting in Washington ahead of a G20 meeting in June.
The FT said Labour's manifesto could also commit to diverting some of the proceeds into aid for poorer countries - in line with a mounting campaign for a "Robin Hood tax" on the banks.
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