At last, an exit strategy for the PM: can he really be eyeing UN's top job?

Call it the ultimate exit strategy. A $400,000 (£215,000) salary plus expenses, a rent-free townhouse on Manhattan's East river instead of a mortgage in Bayswater, and freedom from those troublesome backbenchers. Add world travel and loads of goody bags for Cherie, and Tony Blair could well be tempted by the job of UN secretary general, which just happens to fall vacant at the end of this year.

Sounds far-fetched? It is, because Britain is one of the five veto-holding powers on the UN Security Council. Nobody from the five big powers has ever been head of the UN, whose secretary general has always hailed from a biddable small state so that he or she won't get ideas above their station.

And the big five are the ones who actually pick their servant, the secretary general, even though the full 15-member Security Council takes the decisive vote. Naturally, the five permanent members want the ideal candidate to be more secretary than general.

So why did the speech that Mr Blair delivered in Georgetown yesterday read like a job application? He sounded so convincing in his advocacy of UN reform that he has already been forced to deny to reporters that he would like to take over from the Ghanaian UN chief, Kofi Annan. Mr Blair's friend, Bill Clinton - whose name has also been jokingly linked to the top UN job - has said the Prime Minister would make a "good" secretary general.

The fact is that at this stage in the selection process, the big five are stuck. None of the three declared candidates from Asia - a Sri Lankan, a Thai and a South Korean - has caught the imagination, and no consensus emerged from the first private discussions of the big five on the matter. Although the Asian states continue to insist that this time it is "Asia's turn" for the top job, the Americans and British say the "best" candidate should go forward.

Two alternative candidates from eastern Europe (Latvia and Poland) have been rejected, by veto-holding Russia. China is said to be holding out for an Asian secretary general. It is at moments like this when the first real contenders step out of the shadows and into the limelight to claim the crown.

But would the Security Council tear up its own (unwritten) rules by considering someone from their own inner circle? And how would Britain's colleagues on the Security Council - not to mention the Arab representative - react to the candidacy of the man who brushed aside the UN in his haste to invade Iraq and overthrow Saddam?

So Gordon Brown shouldn't hold his breath if he hopes that Mr Blair could be about to cross the pond for the mother of all cocktail parties. As one senior UN official put it yesterday: "Blair? No way, Jose!"