Lord Mandelson will never get the keys to No 10

His political transformation is now all but complete. Gordon Brown once looked crushed when he was told he had "gone from Stalin to Mr Bean".

Peter Mandelson has gone the other way: from Rasputin to Labour's 007. On his final evening he leans on the railings of the luxury yacht as it bobs about in a Greek harbour, sips a cold Martini and glances down at the newspaper. Back at home they are talking of him as a potential Prime Minister. He arches an eyebrow, casts a final look at the bronzed beauty beside him and thinks "Never Say Never Again."  

Yet as he arrives back in London today, Mandelson's holiday dreams are likely to fade faster than his tan. His unique mixture of suave charm and icy menace may have helped him escape political death on more than one occasion but he is now at the peak of his powers. "PM" is never going to become PM — and in his heart he must know it.  

He shouldn't be denied his moment of self-satisfaction. For a decade the media have attacked him for a multitude of sins, some real, many imagined. He has been written off more often than anyone can remember. For the first time, there are now journalists and commentators who rate his prospects of success more highly than he does himself. But Mandelson is no fool.

He has been around long enough to recognise the mood of unreality that so often engulfs Westminster at this time of year. This week he is at the peak of his power. Not merely First Secretary but deputy prime minister in all but name and now acting Prime Minister too. He would have achieved none of those things had he not tied his fortunes so completely to Gordon Brown.  

In reality, Brown is still in charge in Scotland, where he often is at weekends anyway. Mandelson was no more running Britain from his Blackberry in Corfu than Harriet Harman was with last week's self-aggrandising meetings at Number 10. The Downing Street officials who keep the country ticking over in August regard the "who's really in charge?" brouhaha with amusement not concern.

They are happy for Ms Harman to knock off early most afternoons and for Lord Mandelson to stay on the yacht for that extra day. It keeps them out of their hair. If there is an important decision to be made it is to Mr Brown that they will turn every time. 

Mr Brown's leadership is more secure today than at any time since the botched election-that-never-was of 2007. If the man best placed to take over from him really is Lord Mandelson then the prime minister can sleep easy at night.  
To be in the running Mandelson would have to relinquish his peerage. That would provoke a leadership crisis and Mandelson would be in no position to take advantage of it. He would still need a safe seat that could be won with certainty at a by-election. No Labour seat is safe enough for that, least of all if the sitting MP were to make way for him. Voters hate being asked to go to the polls just for the convenience of politicians. And the chances of potential rivals in the Commons sitting on their hands while he tried to get back in are close zero.  

Everyone is entitled to their dreams.  But Mandelson's Lazarus-like resurrection, when Brown invited him back into the Cabinet last October, was enough of a dream come true. It is fanciful to believe he can go any higher. 

Might he then become leader of the Labour party after the election, when the job is unlikely to include the added bonus of being PM? Again the answer is no. Even if he wanted to, and that seems unlikely, he would still need to find a seat, win it, and take on all challengers in a leadership election. Mr Blair's wish that one day the party would come to love Peter Mandelson has not come true.

They may have come to respect him, even to be grateful to him for steadying the ship before it went down, but Labour members, whether in Parliament, the constituencies or the unions, are not about to put him in charge. 

For the first time in his political career, Mandelson's better qualities are in evidence: his steadiness in a crisis, his ability to communicate a sense of purpose, his humour and refusal to despair. Thanks to the media that once reviled him, he now appears positively avuncular. But he knows that if he were ever to put himself in contention for the leadership they would turn on him again.  

Everything that could be trawled up to discredit him would be. His history of spin, the deceptions and bad judgment that led to him having to resign twice from Mr Blair's Cabinet and, yes, his sexuality. The Right-wing tabloids may have given up the worst excesses of gay-baiting but they would find plenty of ways to suggest Britain wasn't ready for a homosexual prime minister.  

As the party conferences approach there will be no shortage of leadership speculation. If Labour's poll ratings don't improve dramatically the question will be asked once more: could anyone do better? But the chance to replace Mr Brown has passed. It won't come again. Mr Mandelson may feel flattered that he's spoken of as a potential Prime Minister but he should be realistic enough to know that it isn't going to happen. 

Lance Price is a former Labour Party director of communications. His next book, Where Power Lies, a history of Downing Street's battles with the media, is published next year.