David Cameron will face the biggest backbench rebellion since he became prime minister on Monday, as the House of Commons votes on whether there should be a referendum on EU membership.
Up to 70 Conservative MPs have signed a motion defying a government three-line whip, which orders them not to vote in favour of a national vote on whether to stay in the EU. Britain hasn't had the chance to decide on its place in Europe since 1975.
Conservative sources have warned that there could be resignations over the issue - and one ministerial aide to the Northern Ireland secretary has already said he could quit over the vote, telling the BBC it is a “question of putting country and constituency first”.
Labour and the Liberal Democrats have also whipped their backbenchers to vote against the motion, meaning it has little chance of going through.
William Hague will lead the debate and the prime minister will be in the chamber for the vote as he attempts to face down his backbenchers.
On Monday morning he said it was the "the wrong question at the wrong time" and warned backbenchers not to "put up some graffiti about on a Thursday afternoon, to pass a motion which they then say doesn’t matter".
Mark Seddon of the People's Pledge, a cross-party campaign group calling for a referendum on Britain’s membership of the EU, says attempts by all three parties to force their MPs to vote against a referendum are “Kafka-esque”: “If I hear another politician in Westminster banging on about democracy in Tahrir Square, I think I’ll start counting the spoons.”
Yesterday Ed Miliband told the BBC the prime minister had brought his troubles on himself: “Over the last six years, what has David Cameron done? He’s appeased the eurosceptics in his party – he’s brought tomorrow’s events on himself."
The internal Tory row comes at the same time as turmoil in the eurozone - and Cameron is reported to have had a bust-up with French president Nicolas Sarkozy during a summit in Brussels.
According to diplomats, French president is said to have told the PM: "We are sick of you criticising us and telling us what to do. You say you hate the euro and now you want to interfere in our meetings."
The two clashed over whether or not all 27 countries in Europe would attend a summit on Wednesday, where a solution to the euro crisis is expected to be announced, or if just the 17 countries in the euro would attend.
Cameron has cancelled planned trip to Japan and New Zealand to attend the meeting - and he told Sarkozy a deal would not hold sway if all 27 countries were not involved in solving the eurozone crisis.