David Cameron risked inflaming his party yesterday when he admitted tacitly that it would be too difficult to hold a referendum on the EU reform treaty once it comes into force.

The Tory leader is under pressure from MPs and activists to pledge to give the British people a vote on the treaty even if it has been ratified by all 27 EU member states. So far more than 40 Tory MPs have signed a Commons motion calling for a referendum “before or after ratification”.

Mr Cameron refused to give the commitment insisting that he would devote his energy to securing a poll while “the treaty is live and being debated”.

“I’m not going to do anything that undermines the focus we have right now to fight for that referendum,” he said. “The time for a referendum is now,” said Mr Cameron, before effectively ruling out a plebiscite once the treaty comes into force, scheduled for January 1, 2009.

“There is no doubt that it’s easier to hold a referendum when it is front of people not just in this country but in other countries as well.”

Mr Cameron sought to reassure Eurosceptics that he would not renege on his promise to pull out of the European People’s Party despite a strengthening relationship with Angela Merkel. Mr Cameron is due to spend Friday in Berlin at a meeting with the German Chancellor, whose CDU party is the senior partner in the centre-right grouping in the European Parliament that is judged too federalist by most Tory MPs.

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