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European parliament elections will challenge ToriesReuters

It is hard to overstate the importance to Prime Minister David Cameron's prospects of this May's European parliament elections in which, according to the latest poll, he may well come third.

Ever since he moved to shut down the Euro rift that has fundamentally split his party for decades, by promising an "in-out" referendum in 2017, he has failed to see his hopes realised.

Eurosceptic backbenchers banked the pledge and immediately, and predictably, moved on to the next set of demands. The latest were contained in the private letter signed by around 95 Tory MPs calling for a veto of all new EU regulations.

Now the MPs have been rebuffed by Cameron, they are pressing for clear, specific proposals included in the Euro election manifesto on exactly what he plans to renegotiate with Brussels.

Their intransigence has already seen Cameron forced to recognise that all his attempts to shut down the row and finally stop the party constantly "banging on about Europe" will likely end in failure.

The splits were always going to widen as this May's European parliament elections approached, but they have now reached such a level that Chancellor George Osborne was forced to deliver another keynote speech warning about the UK's possible withdrawal from the EU.

But it simply hasn't, and never will, work.

Many, possibly even the majority, of Eurosceptic rebels want the UK out of the EU and will be satisfied with nothing less. And no one believes Cameron would ever back an "out" campaign, virtually irrespective of what reforms he negotiates with Brussels.

Osborne's speech has done nothing to persuade the sceptics not to ramp up the pressure on the prime minister, with repeated demands for a clear statement from him on his red lines in negotiations with Brussels and continued rumblings about the benefits of an election pact with Nigel Farage's Ukip, championed by the likes of MP Peter Bone in his interview with IBTimes UK and echoed in the Daily Mail.

The latest opinion poll, by YouGov for the Sun newspaper, added to Cameron's misery by suggesting the Tories are on course to come third behind Labour and Ukip (23%, 32% and 26% respectively). The only upside from such a result would be for Labour, who would have seen off the often-predicted victory by Ukip.

Nigel Farage
EU poll could boost Nigel FarageReuters

Former minister and leading backbencher Liam Fox did nothing to calm Tory jitters, stating "anything could happen" in the poll and repeating his call for a wider debate on Britain's role within the EU.

Any result which puts the Tories behind Ukip in the Euro elections will spark an instant crisis for Cameron, even if it is accepted that the result will not translate into a similar performance in the general election.

His backbench rebels will declare "told you so" and further turn the screws on the leadership with more demands for red lines, deals with Ukip and even, albeit least likely and entirely unrealistic, calls for him to go. His aim will be to close the door on the poll and focus the party's sights on the general election a year later.

But whatever the rebels do, the one thing they most certainly will not do is keep quiet, even if their antics start to threaten the party's chances at the general election.

There have always been significant numbers who put their anti-EU stand before electoral victory, believing losing a general election may be just what is needed to force the party to realise its only future is on a platform of EU withdrawal.

So Cameron is facing a genuine crisis point this May. And there are no indications yet of how he plans to either avert it or deal with it when it hits beyond keeping his fingers crossed and hoping the Ukip threat disappears.