To some, it is the solution to many of the world's financial woes, raising billions from the financiers seen as responsible for the crises.
But to David Cameron, a share transactions levy – the so-called Tobin tax – is a dagger aimed at the City of London that he will resist at seemingly all costs.
The Prime Minister said in an interview with the BBC yesterday that he would block a Europe-wide Tobin tax, setting the scene for another clash with the French President Nicolas Sarkozy. Mr Sarkozy wants the Tobin tax to be on the agenda of a European summit in Brussels on 30 January.
"If the French themselves want to go ahead with a transactions tax in their own country, then they should be free to do so," Mr Cameron said. "I don't think [it] is sensible."