In a remarkably frank interview with The Times, the one-time bogeyman of Eurosceptics also predicted that Britain would stay out for years, not least because Gordon Brown was so “passionate about his contempt for Europe”.

In another startling admission, the veteran French leftwinger said that the European Union was in a “state of latent crisis” because of weak leadership. He blamed member state leaders, including President Chirac of France, for putting national interests before the common good.

M Delors, 78, also spoke with unexpected admiration of Baroness Thatcher, his old nemesis. He said that she was a “figure who counts” in British and European history, and the way her Conservative colleagues dumped her was an example of the “atrocious” manner in which male politicians treat female colleagues.

But his most surprising comments were on the euro. He lamented that EU leaders had failed to heed his warning that monetary union must be matched with close co-ordination of economic policies, and argued that the euro was consequently less attractive than it could have been.

“Since we have not succeeded in maximising the economic advantages of the euro, one can understand the British . . . saying, ‘Things are just fine as they are. Staying out of the euro hasn’t stopped us prospering’,” he said.

Denis MacShane, the Minister for Europe, said M Delors’ comments, vindicated the Government’s “sensible decision . . . to make economic conditions rather than ideology the central issue as far as the euro is concerned”.

But Michael Ancram, the Shadow Foreign Secretary, said: “This is an extraordinary admission by M Delors. If a champion of European integration says that the euro hasn’t worked, it shows how right Britain has been to stay out, doubly so if a more harmonised economic policy is proposed as the way forward. ”

M Delors led the Commission for ten years, pushing through both the single market and the 1991 Maastricht treaty on monetary union, and has just published his memoirs. He spoke warmly of Britain, though he called its aversion to Europe “a great mystery of history”. But he was sharply critical of his own country. He deplored the opposition in France to the EU’s imminent enlargement and President Chirac’s attempts to lay down the law to the former Soviet bloc states because of their pro-American leanings.