Britain's exposure to the International Monetary Fund could rise to up to £40 billion without a Commons vote, Treasury Chief Secretary Danny Alexander has said.
The UK's IMF lending commitments are currently £29.4 billion, but Prime Minister David Cameron has indicated his willingness to increase that figure under plans to significantly increase the support available to ailing economies.
Mr Alexander said the Government could raise its contribution to £40 billion without seeking MPs' approval. Treasury sources said that amount had already been authorised by parliament.
Speaking to BBC1's Andrew Marr Show, Mr Alexander said: "We have two sorts of money that we give to the IMF. There's a £20 billion ceiling for each, so there's a maximum of £40 billion that we can make available to the IMF.
"Currently only about £5 billion of that is actually in use, so we have the capacity to go up to that £40 billion ceiling."
Tory MPs have called for a Commons vote on any further extension of Britain's commitments to the IMF, warning that they would effectively serve as an indirect bailout of the debt-laden eurozone.
In July, 32 Conservative backbenchers defied the Government to vote with Labour against an increase in Britain's contribution to the IMF.
Mr Alexander said: "No country in the global economy can be an island, we are in an enormously inter-dependent world. We have to play a role as a global leader, as one of the largest economies in the world."
But shadow business secretary Chuka Umunna called for detail on the Government's plans, saying Mr Alexander's comments were "not very clear".
"We need the detail. It's the usual practice after a summit of this type for the Prime Minister to come to the House of Commons and give the details, and it's the detail we need here because we are not very clear from what Danny Alexander said this morning, what the commitment would be," he told BBC1's The Politics Show.