Mr Brown insisted last night the group was banned from looking at further “institutional change”. 

But French president Nicolas Sarkozy – whose brainchild it is – said its job was to discover “the new European dream”. He added: “I want a politically integrated Europe.” The group’s formal task is to look at what shape the EU should take between 2020 and 2030. Tory Shadow Europe Minister Mark Francois accused the Prime Minister of failing the British people.

He said: “He signed the renamed EU Constitution without any democratic mandate. He offended everyone by arriving late. And he has opened a Pandora’s box by agreeing to a Reflection Group with no clear remit, chaired by a Spanish Socialist.

“Gordon Brown has failed Britain at this summit. If this discredited Prime Minister does not keep his promise to let the British people make the choice in a referendum, trust in his Government will evaporate.”

In another sign of Mr Brown’s growing isolation in Europe, missing from the summit’s final declaration was a demand by Britain that the Wise Men rule out any further big changes for the next 10 years. Neil O’Brien from think-tank Open Europe said: “Gordon Brown knows that the group he has endorsed will lead to yet another round of integration and more new powers for the EU. He must now rule out a further handover of powers.” 

Bizarrely, former Dutch footballer Johann Cruyff has been tipped as another member with Britain represented by ex-trade union boss John Monks.

Meanwhile, Mr Brown’s allegedly rude behaviour, turning up three hours late, to sign the Lisbon Treaty in Portugal continued to dominate conversations in Brussels yesterday.

EU Commission president Jose Manuel Barroso was said to have told friends that he was “disappointed” with Mr Brown.

He added that he had believed in British punctuality and politeness but the Prime Minister’s behaviour showed that British manners had apparently changed.

Mr Brown also received a humiliating rebuke from former Cabinet colleague Peter Mandelson. Mr Mandelson, shortly to give up his job as a European Commissioner, claimed that Mr Brown was losing the argument over Europe.

Asked by the BBC if he would like Mr Brown to put the case for Europe more positively, he said: “In politics you don’t win an argument by putting yourself on the back foot.”

Meanwhile, it also emerged yesterday that MPs will only get a “take it or leave it” vote on the Lisbon Treaty.

And they will not be allowed to demand detailed amendments, despite the debate scheduled to last 21 days, almost 10 per cent of the parliamentary year. 

The EU summit also agreed to send administrators and police to Kosovo ahead of an expected declaration of independence from Serbia. It also issued a tough declaration on Iran.