George Osborne is facing anger from Tory backbenchers and Labour after announcing Britain is to commit another £10 billion to the IMF.
The Chancellor insisted the increased funding was vital to protect jobs and growth in this country.
But critics said he was putting the taxpayer on the hook for more bailouts of the struggling eurozone. He was also accused of dodging a potentially embarrassing parliamentary vote on the extra contribution.
Finance ministers and central bank governors struck the deal - which should boost the IMF's resources by 430 billion US dollars (£267bn) - at a meeting in Washington. Alongside the UK's increase, Japan is to contribute an extra 60 billion dollars, South Korea 15 billion dollars, Switzerland 10 billion dollars and Australia seven billion dollars. However, the United States and Canada have refused to add any more into the pot.
Mr Osborne said: "The UK sees itself as part of solution to the challenges facing the global economy, not part of problem. We are helping to solve the global debt problem rather than adding to it. Jobs and growth in Britain depend on stable world economy. That needs a strong IMF."
IMF managing director Christine Lagarde said: "We warmly welcome pledges by our members to increase IMF resources by over 430 billion dollars, almost doubling our lending capacity. This signals the strong resolve of the international community to secure global financial stability and put the world economic recovery on a sounder footing."
Shadow chancellor Ed Balls accused Mr Osborne of signing up to a "sticking plaster" deal and "running scared" of parliamentary scrutiny.
Tory MP Douglas Carswell branded the decision "madness" and "IMF bailout bull". Writing on his blog, he suggested the loan "makes you wonder how all those earlier bailouts have worked out".
Mr Osborne told BBC Radio 4's Today programme: "When you look at the Tory backbench opinion, of course some people have been critical and they have been critical all along, but actually quite a lot of Conservative backbenchers have come out and said this is the necessary and right thing. I think there is a broad body of Conservative opinion that understands we are doing the right thing."
The Chancellor accused Labour of being "opportunistic", arguing that they had supported the IMF in the past.