Brown told G20 finance ministers that ‘a global financial transactions levy’ would be one way ‘to reflect the global responsibilities of financial institutions to society.’

Although the British premier warned of the need to avoid ‘prohibitive costs’ on the banking sector, he added: ‘I do not think these difficulties should prevent us from considering with urgency the legitimate issues.’

Brown also stressed that his country would not act alone on the issue of what is often called the Tobin Tax, saying: ‘Let me be clear: Britain will not move unless others move with us together.’

The comments represent a strengthening of Brown’s position on the tax. Previously, Britain was thought to be opposed to the idea because of fears it would damage the City of London, Europe’s largest financial district.

Debate over new versions of the Tobin Tax has accelerated since the financial crisis erupted last year, with France among nations leading calls for its introduction.

The tax was originally proposed in 1971 by Nobel Prize laureate James Tobin as a means of reducing speculation in global markets, but Tobin himself later began to doubt his own idea was workable.