George Osborne is prepared to face down Tory backbenchers in order to increase Britain's contribution to the International Monetary Fund, Downing Street has said.

A spokesperson for the prime minister said on Wednesday that the Treasury would consider any "decent request" made by the IMF for extra money, although the exact figure was not yet known.

But they insisted that the fund was designed to rescue "countries not currencies" and said it was not up to Britain to rescue the euro. "This money is not a substitute for the eurozone providing resources to back up its own currency," she said.

It has been reported that the IMF wants to increase its ability to lend from $385 billion available to $885 billion, factoring in a buffer zone that means it needs to ask its member countries to stump up $600bn.

Britain contributes 4.5% of IMF funding and an increase could see its contribution exceed the $40bn ceiling currently imposed by parliament.

To increase the amount of money provided to the IMF, George Osborne would have to seek the approval of MPs, something he indicated on Monday he would be willing to do.

"Britain has always been prepared to provide the resources in the past and will be willing to provide the resources in the future if there is a strong case," he said.

However he could face a tough time pushing the measure through the Commons as eurosceptic MPs could join forces with Labour to defeat the move.

Tory MP Douglas Carswell warned ministers that they "cannot rely on a majority", while Wycombe MP Steve Baker told City AM they would “give very serious consideration to voting against the government".

Last July, 30 Tories rebelled when the coalition asked MPs to approve another £9bn for the IMF. The government only won the vote with a majority of 28.