The Liberal Democrats are preparing to include a "Robin Hood Tax" on the banks in their manifesto when it is launched on Wednesday, says a source familiar with the take-from-the-rich campaign.
The move would align the party with a campaign that has attracted high profile showbiz supporters, including Bill Nighy and Sir Ben Kingsley, who have both made videos promoting the idea.
Although the Liberal Democrats Treasury spokesman, Vince Cable, has already come out in favour of a 10 per cent levy on bank profits, this will be the first time a mainstream political party has embraced the idea of a small tax on the trillions of pounds of inter-bank financial transactions.
The Conservatives also back special taxation on banks, not least to pay for tax breaks for married couples; the Government introduced a windfall tax on banker's bonuses last year, which raised £2bn and which has now lapsed. The Chancellor, Alistair Darling, has spoken favourably about a financial transactions tax, but the proceeds would go into general government funds, including defence spending.
The Robin Hood Tax campaign wants the proceeds to be earmarked for redistribution to the poorest here and abroad, to support the NHS, plus overseas development and projects to fight climate change.
Under a mandate from the G20 leaders, including Gordon Brown, the International Monetary Fund is examining options for a global financial transactions tax, which would be presented at the annual IMF meeting in Washington on 20 April.
Among the big parties, the Liberal Democrats are now making most use of the financial crisis for political purposes, and tapping deep public anger about the City's ways. The party has stepped up its attacks on the financial sector in recent weeks, with Mr Cable describing those who threatened to leave the UK in response to tougher regulation and higher taxes as "pin striped Scargills".
The campaign is arguing for an international levy on deals between banks that could start as low as 0.005 per cent on currency exchange and derivatives trading – 5p for every £1,000 of transaction – which could raise $400bn a year. Critics say the tax would erode bank profits while they are still trying to rebuild their financial strength, and costs would be passed on to bank customers anyway.
The campaign is supported by Oxfam, TUC, Barnardo's, The Salvation Army, Friends of the Earth, ActionAid, RSPB and Crisis.
A new short film supporting the campaign shows Sir Ben being mugged. The star of Gandhi and Shutter Island is cornered in a dark car park by a group of "Robin Hoodies" and forced to hand over his possessions.
"At a time when people at home and abroad are suffering economic hardship, our politicians should listen to the voice of ordinary voters," he said. "A tiny tax on banks could make a massive difference to poor people."
Professor Sir Tony Atkinson from Cambridge and Professor Sudhir Anand at Oxford are among senior academics from Britain and 34 other nations supporting the tax. Other British academics backing the plan come from Sheffield, Warwick, London, Stirling, Essex, Manchester and de Montfort, and economic thinkers from 35 nations are represented in the list of signatories.
Professor Jeff Sachs of Columbia University, also an adviser to the UN Secretary-General, Ban Ki-moon, said: "The transaction tax is technically feasible and morally essential to repair the mess made by the banks.
"I have long advocated such a tax, as a clear way to raise billions of dollars to fight climate change and to achieve the millennium development goals.
Highlights of the day
Scare tactic of the day
Andrew Charalambous, the Conservative candidate for Edmonton, has left voters in his constituency feeling a little queasy. The Cyprus-born property investor has issued pamphlets, emblazoned with a blood-spattered knife, bearing the slogan: "Labour's cuts. Violent crime up 44 per cent under Labour." So much for positive campaigning.
C eleb of the day
It was Michael Caine standing beside David Cameron last week. Yesterday, it was the turn of Sir Ian Botham, a long-term Tory. But Mr Cameron was keen to point out it was not a political stunt – he was accompanying the former cricketer on part of a walk raising money for charity. Of course.
Comeback of the day
It's not every day that former Tory leaders are lavished with praise by Alastair Campbell. But Labour's former spin chief was delighted to see Michael Howard pop up on Sunday morning television, having led a failed Tory campaign in 2005. "What a joy to turn on the BBC this morning and see Michael Howard on the Andrew Marr sofa," Campbell enthused. "More, more, more please."
Pet name of the day
Cameron has recently been shadowed by ITV News anchor, Mark Austin. Things got off to a shaky start when the presenter seemed unsure about what to call the Tory leader. "So Dave doesn't seem like a sort of old Etonian name to me ... I heard your wife calls you babe?" Realising that may be deemed as over familiar, he concluded: "I probably won't call you babe."
Gimmick of the day
Those imaginative people at the Taxpayers' Alliance have thought of another way to win a bit of publicity. This time, with a"debt clock" recording Britain's rising borrowing. It has been mounted on a huge lorry and will make a 1,300-mile trip around Britain during the election. Value for money?