David Cameron will give Tony Blair a free run if he tries to become the EU’s first president, The Times has learnt.

The Conservative leader has told senior colleagues that they should do nothing to oppose a Blair candidacy if the Lisbon treaty, which creates the role, is ratified later this year.

EU heads of government could choose their first president as early as December if the Irish vote “yes” in an October referendum and the other remaining countries yet to ratify then sign up. Mr Blair, now a Middle East envoy, has avoided openly promoting himself before the selection but is known to be interested in representing the EU on the world stage.

The issue is awkward for Mr Cameron, who has repeatedly refused to answer questions about a Blair candidacy on the ground that the Tories oppose the treaty that creates the post.

If the selection of a new EU president does take place this December it will add to the pressure on Mr Cameron to clarify his European policy. He refuses to say what his party would do if the EU reform treaty completes its ratification in all 27 member states before the election, promising only to set out the position in an election manifesto. Privately, however, he is planning how an incoming Conservative government would cope with the new institutions — such as a fixed EU president — that it creates.

Kenneth Clarke, the Shadow Business Secretary, hinted at such a pragmatic approach this week when he suggested that the Tories would be powerless to reopen the Lisbon treaty once it had been ratified — to the alarm of Tory Eurosceptics.

Brussels experts put Mr Blair’s chances of getting the job at 50-50. His closest advisers are urging him to continue to sit tight, warning that any open campaigning would backfire. “They know he is there. They know he would like to do the job. They know who he is, what he has achieved. Do nothing and hope it will come your way would be the best advice for him,” one ally said.

Gordon Brown would support a Blair presidency warmly, The Times has been told, but friends of both men say that it would be in Mr Blair’s interests for the advocacy of his case to come from other leaders.

A senior Tory said: “There have been a number of ‘what if’ discussions and the feeling is that we have nothing to gain in being seen to try to block Blair.”

Some Conservatives say that Mr Blair’s economic liberalism and Atlanticism make him a more attractive candidate than any other possible contenders. “Frankly we could do a lot worse,” one well-placed figure said.

Mr Cameron’s spokeswoman declined to be drawn on his attitude to a Blair candidacy. “We do not accept the need for an EU president,” she said.

Mr Blair’s chances of winning the presidency rose in the first part of the year as other possible candidate fell by the wayside. Jean-Claude Juncker, the Prime Minister of Luxembourg, saw his chances decline sharply after falling out with a key sponsor, President Sarkozy of France. Anders Fogh Rasmussen, the Danish Prime Minister, who was thought to be the favoured candidate of Angela Merkel, the German Chancellor, has taken a job as Nato’s secretary-general.

Significant doubts remain about whether Mr Blair could command enough support among the 27 EU nations, however. Experts believe that he would struggle to win the support of European socialist parties. President Sarkozy, who had been supportive of a Blair presidency, is reported to have cooled on the idea. He is said to have switched support to Felipe González, former Prime Minister of Spain.

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