Gordon Brown will diminish Britain's international role in global financial institutions by increasing European Union representation, as the price for an agreement at the G20 summit

Joaquin Almunia, the European commissioner for economic and monetary affairs, told The Daily Telegraph that in future the EU would have "one voice" in reformed institutions such as the International Monetary Fund (IMF). "For me the most important thing is to have one European voice and position on these bodies," he said.

The Spanish EU commissioner predicted that the Prime Minister would achieve a major success by increasing the IMF's resources to more than $500bn (£353bn) at the summit later this week.

But, Mr Almunia stressed, in return China and other developing countries would demand a "voice and representation&…