DAVID CAMERON faces a damaging new split in the Conservative Party over Europe, after he broke a pledge to leave the main centre-right group in the Brussels Parliament within months.

Tory MEPs said that they felt betrayed and that they would quit the European People’s Party (EPP) unilaterally after he announced that he would delay pulling out until 2009.

Mr Cameron retaliated with a warning that any MEP who defied the new party line would be severely disciplined, have the Tory whip withdrawn and be deselected at the next European election.

The rebels were deep in negotiations last night over their next move. One said: “I was personally lied to by David Cameron. He gave me personal promises that . . . he would leave during the honeymoon as soon as he was elected leader, while the press were still writing about his wife’s dress.” However, as the news sank in, the chances of a large-scale revolt faded.

Geoffrey van Orden, MEP for East of England, said: “I am not happy, but I recognise the reality of the situation.”

Nirj Deva, MEP for South East of England, said: “I am deeply disappointed but I will just have to be patient.”

Mr Cameron promised to withdraw from the EPP during the leadership fight with David Davis, his closest rival, who had a more moderate position. It helped him to win the support of many right-wing MPs. He did not set out a timetable but said repeatedly that he meant “within months not years”.

The matter is of huge importance to Eurosceptics, who believe that the arrangement with the EPP makes them part of the Brussels establishment, which they loathe. The decision to stay in the EPP for the time being followed a fruitless six-month search by William Hague, the Shadow Foreign Secretary, for any mainstream parties in the EU willing to leave the group and join a new one.

This week the only possible partner, the Czech Civic Democratic Party, said that it was too busy forming a government coalition at home to leave the EPP. That left Mr Cameron with the choice of fulfilling his pledge, forcing Tory MEPs to sit alone, or staying within the EPP. Going it alone would leave Tory MEPs sitting alongside other independents such as allies of the far-right French politician Jean-Marie Le Pen. Sources close to Mr Cameron said that this would leave the party open to accusations of extremism. One said: “We would have been sitting with MEPs no one else wants to sit with and that is not where modern Conservatives should be.”

At a hastily arranged meeting with MPs in Westminster Mr Cameron called for unity, saying the party was “back in the game” and a row over Europe would jeopardise the progress made so far. He was rewarded with the customary desk-banging, but MPs present said that a “silent minority” were clearly fuming.

Two MPs, David Heathcoat-Amory (Wells) and Douglas Carswell (Harwich and Clacton), spoke out against the decision. Mr Heathcoat-Amory said it was a matter of trust.

Embarrassingly for Mr Cameron, the MPs who spoke in favour of his delay were from the small remaining band of pro-Europeans: John Gummer, Ian Taylor and Alistair Burt.

Although the Tories and Czech Civic Democratic Party signed a deal yesterday to form a new grouping after the next European elections in 2009 there are serious doubts that it will ever happen. European parliamentary rules mean that any new grouping must include MEPs from five different groupings and there is no guarantee that the Tories will be able to find enough members, unless they resort to independents.

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