In a speech to both Houses of Congress, Mr Brown will call on the US not to turn in on itself, warning that the financial problems facing them are global and can be dealt with only if they "seize the moment" and resort to international co-operation.

The Prime Minister will attempt to speak on behalf of the European Union as a whole when he says that - for the first time in living memory - the entire region is united in wanting to work with America.

Aiming his message in particular at any Congressmen harking back to transatlantic rifts with France and Germany over the Iraq invasion, he will say: "There is no old Europe, no new Europe, there is only your friend Europe."

In an upbeat message at a time of plummeting stock markets, repossessions and redundancies in the US as in Britain, Mr Brown will predict a doubling in the size of the world economy over the next two decades, with sharp growth in business opportunities, prosperity, jobs and incomes.

"We should have the confidence that we can seize the opportunities ahead and make the future work for us," Mr Brown will say.

"Because, while today people are anxious and feel insecure, over the next two decades our world economy will double in size. Twice as many opportunities for business, twice as much prosperity, and the biggest expansion of middle-class incomes and jobs the world has ever seen."

Making his call for international cooperation, he will say: "America knows from its history that its reach goes far beyond its geography. For a century you have carried upon your shoulders the greatest of responsibilities: to work with and for the rest of the world.

"And let me tell you that now more than ever the rest of the world wants to work with you.

"And if these times have shown us anything, it is that the major challenges we all face are global. And let me say that you now have the most pro-American European leadership in living memory.

"A leadership that wants to co-operate more closely together, in order to be a stronger partner for you. There is no old Europe, no new Europe, there is only your friend Europe.