An historic vote on pulling Britain out of the EU could be held next year, throwing all other political calculations ahead of the 2015 general election into chaos.
Tory MP Adam Afriyie, recently tipped as a future party leader, is to launch a bid in parliament next week to force the government to bring forward its promised 2017 referendum to October 2014.
If his plan works, a straightforward "in or out" question would be put to the country just six months before the general election campaign kicked off and would have the potential to oust current party leaders and force the re-writing of the parties' manifestos.
All three party leaders would join the "in" campaign and, if it were lost as current polling suggests it would be, Prime Minister David Cameron would have no option but to resign. If it were won, he would emerge stronger. But it is not a risk he wants to take.
Either way it is a nightmare scenario for senior politicians from all three big parties and they have dismissed the call, suggesting it has no chance of winning a vote in the House of Commons and that time should be given for the prime minister to try renegotiating the UK's position in the EU before the 2017 vote.
But there is one scenario under which it could still happen. And it relies on Labour leader Ed Miliband, whose readiness to spring big, popular, political surprises has been dramatically on display this autumn.
Miliband is being urged by senior MPs, led by former party elections coordinator Tom Watson, to seize the moment and back Afriyie's move when launched in the Commons and then vote for it in November.
That seems unlikely as it would represent a significant U turn. But it is possible Miliband could order his MPs to abstain on the vote, leaving the Tories once again to tear into one another over the issue, which has dogged them since the time of Margaret Thatcher's premiership and which helped bring her down.
In those circumstances it is possible that enough Tory rebels would back Afriyie's move to get it through the Commons, landing the prime minister with a leadership-threatening crisis. The last similar vote saw 81 Tories voting against their leader which could be enough to defeat him.
Cameron aides insist there is no way the prime minister will let any of this happen and are even threatening that, if the rebel motion were carried, they would pull the entire Bill setting up the 2017 referendum.
They also believe that Afriyie will be seen as a trouble-maker more interested in promoting himself than in strengthening the prime minister's hand, as he claims his move would do, and that would unite the party behind Cameron.
Afriyie insists he is not self-promoting, declaring: "I would not be able to sleep at night if I do not bring forward this opportunity for the British people to have a say."
His proposal would give Cameron 12 months to renegotiate Britain's role with the rest of the EU before the referendum, he said.
Miliband aides have so far suggested they want to see exactly what it is Cameron wants to renegotiate before Labour commits itself on the referendum. But this latest development has offered Miliband an opportunity to further embarrass the coalition government, at the very least.
The EU issue has haunted Conservative governments for decades and has been thrown into sharp focus by the UK Independence Party and its charismatic leader Nigel Farage, which is threatening to split Eurosceptic votes at the next election and deprive the Tories of victory.
Cameron believed he had effectively killed off the issue by offering the 2017 vote but Afriyie said that people did not trust Cameron to go ahead with it.
"Many people think delaying the vote is just a tactic to allow all the political leaders to kick the can even further down the road," he wrote in the Mail on Sunday.