David Cameron has indicated MPs will not be given a vote on increasing Britain's contribution to the International Monetary Fund, avoiding a potentially embarrassing Commons defeat.
Speaking at a press conference at the G20 summit in Cannes, the prime minister said this could be done as a previous increase voted on by MPs gave "headroom" for Britain to supply more money to the IMF.
He said any additional money would be "within the limits that have already been agreed by Parliament".
But the secretary of the backbench Tory 1922 Committee Mark Pritchard told Huffpost UK on Friday afternoon: "There needs to be as much speed on the Eurozone tackling its huge deficit and becoming globally competitive as there is on the speed of the German-Franco pact asking the British taxpayer for yet more money.
"This is a back-door bail out in all but name."
Cameron will want to avoid a vote in Parliament on the issue as it is likely an alliance between Labour and disgruntled eurosceptic Tory backbenchers could inflict a damaging defeat on the government.
The previous vote in July that increased Britain's contributions passed the Commons with a majority of just 28, with 32 Conservatives joining Labour in voting against the government.
And last Monday 81 Tory MPs defied a three-line whip to vote in favour of holding a national referendum on Britain's membership of the European Union.
Many more were sympathetic to the rebels' view and there was widespread unhappiness at the way Downing Street browbeat MPs into voting the way it wanted them to. Government whips were caught out before the vote - they had privately expected only about 50 Tories to rebel.
Cameron said it was up to the eurozone nations such as Germany and France to rescue the euro.
"Britain will not contribute to the eurozone bailout fund and we’re clear that the IMF will not contribute to the eurozone bailout fund either," he said.
He added: "Britain will not invest in the IMF so the IMF can invest in a eurozone bailout fund."
"The IMF does however have a vital role to play in supporting countries, right across the world, that are in serious economic distress.
"It is essential for confidence and economic stability that the IMF has the resources it needs so the G20 has made clear that it is willing to increase IMF resources as necessary to provide a boost to global confidence.
"Alongside other countries, Britain stands ready to contribute to the effort, within the limits that have already been agreed by Parliament.
He added: "But let's be clear: global action cannot be a substitute for concrete action by the eurozone to stand behind their currency by implementing what they have agreed and resolving the uncertainty that remains in Greece and elsewhere."