Fans of Tony Blair and Peter Mandelson, who mourn their departure from the political frontline, will be dancing with joy.

Two of the founding fathers of New Labour could make a spectacular comeback on the world stage in the next few years. I reported last month that David Cameron is prepared to back Mandelson as the next director general of the World Trade Organisation, raising the prospect of a fourth comeback by the former Prince of Darkness.

One senior diplomatic source said that Downing Street is deadly serious about lining up Britain's former European trade commissioner for one of two posts:

• The next director general of the WTO after the Frenchman Pascal Lamy stands down next year. Britain believes France will support a British candidate after George Osborne provided early – and decisive – backing for Christine Lagarde as the managing director of the IMF.

• The EU's high representative for foreign affairs if Baroness Ashton decides to throw in the towel before her term ends in 2014. Ministers, who are supportive of Ashton in public, believe she is struggling. They would not be surprised if she stands down. Mandelson had wanted the job in 2009 and believes Gordon Brown let him down by failing to back him.

This is what the diplomatic source told me about Mandelson:

Of all the figures associated with New Labour Peter Mandelson is the one figure who is on Downing Street's radar. David Cameron and George Osborne are serious about finding him a big job. The WTO post is coming up. But Peter Mandelson would be an obvious candidate to succeed Cathy Ashton if she stands down. Ministers accept that that post would have to go to a Labour candidate between now and 2014 because of the deal with the European Parliament in 2009 [over top EU jobs] when Cathy and Herman Van Rompuy, [centre right president of the European Council], were appointed.

If Mandelson lands a job he may be greeted by familiar face on the world stage. The thought is slowly dawning on ministers and officials that Tony Blair may be the ideal candidate to succeed José Manuel Barroso as president of the European Commission when he retires after two terms in 2014.

This would be a more modest post than the job Blair recently floated. In an interview with the Times to promote the latest volume of his memoirs, the former prime minister said that the EU needs a directly elected president to give the union greater clout on the world stage.

The president of the European Commission is appointed by the heads of government of all 27 EU member states. Barroso often lives in fear of large member states, particularly France.

Whitehall sources say that it is early days and Blair's chances may depend on the outcome of next year's French presidential elections. Nicolas Sarkozy, the French president, would be a strong candidate to succeed Barroso if he loses the presidential election next year. Angela Merkel, the German chancellor, may also like to become the first German president of the commission since Walter Hallstein in 1967.

Blair may also feel that he has had his fill of high European politics. He had hoped to become the first president of the European Council in 2009. But his campaign fell apart when José Luis Zapatero, the Spanish prime minister, vetoed Blair in private. Zapatero will stand down at the next election in Spain.

If Blair enters the frame he will have certain advantages. Unlike Barroso, who hails from a relatively small member state (Portugal) and who was a centre right prime minister, Blair is from one of the "big three" member states and was (if only on paper) a centre left prime minister.

But Blair would have one key disadvantage at a time when the single currency is struggling: Britain is not a member of the euro. But Blair could argue that at least he tried on that front while he was prime minister.