British Prime Minister Gordon Brown surprised G20 finance ministers by urging them to consider a tax on global financial transactions, but the idea got a lukewarm response.

Brown said the levy, often called the Tobin Tax after the US economist who devised it, would force financial inst-itutions to be more respon-sible and was one of a range of measures that could help curb risky behaviour.

It was always thought the UK opposed the idea because of its possible effect on financial centre London.

Just hours after Brown gave the idea fresh impetus at the two-day G20 meeting, the US appeared to shoot it down in flames.

US Treasury Secretary Tim Geithner said his country had not changed its long-held opposition to an idea first floated in the 1970s.

“No, that’s not something that we’re prepared to support,” he told Sky News.

Later, Geithner said “it is fair to say that we agree that we have to build a system in which taxpayers are not exposed to risk of loss in the future”.

But while he refused to say if Washington would actively oppose a levy, his assertion that it was “an idea that has been around a long time” spoke volumes.

Dominique Strauss-Kahn, head of the IMF, the very body which the G20 has asked to study the feasibility of such a measure, was blunt in his assessment.

Introducing a Tobin Tax “is very difficult for a range of reasons, in fact it is impossible”, he said.

The IMF, which is due to give its report next April, is working on producing a different, “better” solution - a tax which would “curb risk-taking in the financial sector” and make bankers “take fewer risks because it will cost them more, while at the same time creating a reserve fund which could be used in a crisis”.