A row has broken out over a possible new tax on banks just hours after Gordon Brown suggested the move, with the US signalling its opposition to the plan.

Speaking as the G20 meeting in St Andrews closed, US Treasury Secretary Tim Geithner said "experience has been mixed" in this area. He added that the US's favoured route was to impose a fee over time on banks which have required public funds.

However, France's finance minister Christine Lagarde said she supported the more radical idea of a tax.

Paying a surprise visit to St Andrews this morning, Mr Brown called for a new "economic and social contract" so that in future banks do not reap all the rewards in good times while taxpayers pick up the bill for bailouts in bad ones.

Calling for debate on the issue, Mr Brown said: "There have been proposals for an insurance fee to reflect systemic risk or a resolution fund or contingent capital arrangements or a global financial levy".

Officials said Mr Brown favoured a levy, effectively a "Tobin tax" imposed on banks' transactions such as equities, derivatives and currency trades.

Last night that goal appeared to be in disarray, as Mr Brown had pledged that "Britain will not move unless others move with us". However, some officials attending the meeting said the US and others might adopt a hostile stance to the tax as a negotiating tactic.

Finance ministers attending the group of rich and developing nations agreed that the International Monetary Fund would assess various ways to force banks to take more responsibility for the systemic risk they pose and report back in April.

These ideas can then be discussed at the G20 meetings next year in Canada in June and Korea in November.

Alistair Darling, the chancellor and the host of the two-day conference in Fife, claimed the meeting achieved a "major step forward" by agreeing a framework which will see individual countries submit growth plans and fiscal policy to the IMF early next year. These plans will be audited by the IMF and subject to peer review.

The hope is that the initiative - which is set to take at least a year - will encourage countries to work together to avoid building up similar global imbalances as in the past and to create a "framework for strong, sustainable and balanced growth".

Critics are sceptical of the plan, because it will require countries to agree on contentious issues such as trade imbalances and exchange rates.

Mr Darling had hoped to make significant progress on how to finance improvements to the environment ahead of the UN's summit in Copenhagen next month. However it proved impossible to thrash out an agreement on how much large countries should pay in subsidies to developing nations not to pollute the environment.

Mr Darling argued much "heavy lifting" had been done in St Andrews, making it easier for progress to be made in Copenhagen.

As widely expected ahead of the event, there was broad consensus that global fiscal stimulus programmes should not yet be withdrawn as the recovery is still too fragile.

In a communiqué issued at the end of the event, the G20 group said: "The recovery is uneven and remains dependent on policy support, and high unemployment is a major concern."

The document added: "We agreed to maintain support for the recovery until it is assured".

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