DAVID CAMERON faced his first diplomatic challenge yesterday as Angela Merkel warned him against pulling out of Europe’s main centre-right grouping.

He also faced criticism for not attending a pre-summit meeting of European conservative leaders in Brussels.

The new German Chancellor put the new Conservative leader on the spot by urging him to reconsider his election campaign promise to leave the federalist bloc formed by the European People’s Party and the European Democrats in the European Parliament.

“I look forward to good and intensive co-operation with you, in particular within the framework of the EPP-ED as a clear base for our bilateral dialogue as partners,” Frau Merkel told him in a letter.

Her letter came days after Kenneth Clarke said that Mr Cameron’s intention of withdrawing from the EPP-ED was a “head-banging” policy. A majority of Tory MEPs also oppose Mr Cameron’s stance.

Mr Cameron was said to have further upset Frau Merkel and Nicolas Sarkozy, the French Interior Minister, by staying away from yesterday’s pre-summit meeting here of EPP leaders, which is often attended by Tory leaders.

Mr Cameron, who did not send anyone in his place, blamed a diary clash for missing the meeting. He instead spent the day on a visit to Northern Ireland.

Had he turned up he would have met Silvio Berlusconi, the Italian Prime Minister, and Mariano Rajoy, the former Spanish Interior Minister, who leads the opposition Popular Party.

Michael Howard, the previous Conservative leader, negotiated a semi-detached relationship between the Tory MEPs and the EPP group, but Mr Cameron is insisting that he will stand by his leadership campaign pledge to withdraw completely.

William Hague, the Shadow Foreign Secretary, indicated this week that he would take some time to decide what todo with the Tories’ 27 MEPs, giving hope to proEuropeans who want to fudge the issue.

Frau Merkel congratulated Mr Cameron on his victory on behalf of her party, the Christian Democratic Union, and expressed confidence in his ability to renew the Tories and lead them back to office.

“I am sure . . . that in the foreseeable future the great tradition of British Conservatives will once more have a good chance to go into government,” she wrote.

But Frau Merkel made clear that Mr Cameron should place Britain at the heart of Europe.

“Great Britain and the British Conservatives are an indisputable element of European politics. In the EU we can work together on our common interests and convictions to safeguard individual freedoms, the regulation of the Common Market, as well as a strong transatlantic cooperation.”

Abandoning the EPP-ED group would reduce the Conservatives’ influence in the European Parliament. The Conservatives currently have a vice-president of the Parliament and chair five of twenty parliamentary committees.

Daniel Hannan, the hardline Eurosceptic Tory MEP, wants the Conservatives to join forces with rightwingers in Eastern Europe because a grouping needs representatives from five countries to enjoy full rights in the Parliament.

Poul Nyrup Rasmussen, the former Danish Prime Minister who is president of the Party of European Socialists, said: “The European Right is deeply divided.

“The EPP has been in danger of splitting for years. Now it is showdown time. It looks like David Cameron’s threat to take the Tories out of the EPP has resulted in a threat from Angela Merkel never to speak to them again.”