LEADERS of three of the most powerful countries in Europe have strongly criticised David Cameron at the EU summit over plans by British Conservatives to scupper the Lisbon treaty.

Nicolas Sarkozy, Angela Merkel and Jose Luiz Rodriguez Zapatero are understood to have privately criticised the Tory leader after he sent a handwritten letter to the Czech president Vaclav Klaus, who is refusing to sign the treaty. The letter was seen as an attempt to influence the Czech Republic, the only country not to have ratified the treaty.

A Tory spokeswoman said “We have never concealed the fact that we sent the letter ... David Cameron has made no secret of its contents. It sets out his public opinion in a private letter.” Senior British sources familiar with thinking at the highest levels of the EU say that the leaders of France, Germany and Spain all raised questions about the Cameron letter. It is understood that Cameron encouraged Klaus to delay the ratification of the treaty by setting out Tory policy to hold a referendum in Britain on the treaty if it has not been ratified by all member states.

The sources have told the Guardian that

— Sarkozy was overheard telling Gordon Brown that he was incensed by Cameron's letter, which the French saw as an attempt to wreck the Lisbon treaty.

— Merkel was also said to be upset by Cameron's letter. The German chancellor is understood to have echoed concerns of senior figures in her CDU party, such as the former European parliament president Hans Gert Poettering, that Cameron's behaviour had been untrustworthy.

Zapatero — who addressed the recent Labour party conference and will have to negotiate directly with Cameron if he wins the election because Spain holds the EU's rotating presidency until July 2010 — made clear to diplomats that he regarded Cameron's letter as damaging and an attempt to scupper the treaty.

The interventions by the EU leaders come as the Tories plan to abandon their two-year campaign to hold a referendum on the Lisbon treaty. Senior Tories told the Guardian that Cameron will set out his thinking in the coming weeks if, as expected, the Czech president finally ratifies the treaty.

It is understood that Cameron will drop his pledge to hold a referendum on the treaty on the grounds that it is impossible to open a treaty that has entered EU law. A Tory government would instead focus on repatriating social and employment laws, in effect restoring the British opt-out from the social chapter. This has been sprinkled around various EU treaties since Tony Blair ended the opt-out in 1997, meaning that its measures could only be restored to Britain with the agreement of all member states.

Brown used his appearance at the summit, where he held a series of formal and informal one-to-one meetings with EU leaders, to launch a strong attack on the Tories' approach to Europe. He said “The Conservative party is standing apart from the mainstream in Europe.”— The Guardian, London