Steve Richards: Neither of these two will lead Labour

In their different ways, Mandelson and Harman have experienced all the oscillations of politics

With Gordon away, Harriet and Peter come out to play. In a series of headline-grabbing interviews, Harman speaks up for women in politics and in the private sector. Making almost as much noise in the summer calm, Mandelson re-frames the debate about Labour's spending plans and suggests sensationally that Brown might take part in televised leaders' debates during the election. Harman was not especially thrilled with Mandelson's ubiquity when she was supposed to be running the country. Friends of Mandelson have suggested that some of Harman's propositions in recent days were barmy.

The duo's hyperactivity has added spice because it is accompanied by speculation that one of them might be the next Labour Party leader. We are possibly witnessing the preliminary skirmishes of a full-throttled leadership contest. Mandelson was given the chance to rule out being leader in a recent BBC interview; he chose not to do so. Harman is the only member of the Cabinet to have won a leadership contest since 1994 when she became deputy leader, emerging triumphantly from a crowded field. She is a formidable campaigner and thick-skinned too, an important quality given the abuse she receives in much of the media.

The re-emergence of Mandelson is already an astonishing story. If he were to become leader, all three founders of New Labour would have been given their chance, Blair first, then Brown and finally the figure who worked so closely with them in the dark days of the 1980s. His elevation would be vivid proof that the younger generation was not up to the job of leadership and was dependent still on those that formed New Labour in the mid-1990s.

Harman's further rise would also expose the lack of political talent among the younger ones that sit around the cabinet table. Like Mandelson and unlike most of the Cabinet, she was battle-hardened in the 1980s, winning a by-election in 1982 as Labour plumbed the depths of unpopularity. In their very different ways, Mandelson and Harman have experienced all the wild oscillations in politics. Most of the potential leaders from the younger generation were special advisers to Blair or Brown, protected from the frontline, functioning behind the scenes, hidden from the media. They are not well prepared for leadership.

There is, though, one big problem with the engaging vision of a Harman-versus-Mandelson contest. Harman has said publicly and unequivocally that she does not want to be the next Labour leader and will not stand in a contest. I have checked in recent days with her closest allies; they tell me emphatically that this remains the case.

If there is a leadership contest before or after the election, Harman will not stand. There are no get-out clauses, no statements about not being able to envisage circumstances where she would stand. She is not going to do so. I am sorry to disappoint those who believe politicians only utter statements with their own future ambitions in mind, but Harman says what she has said because she believes it.

I am told it is possible Harman may wish to remain as deputy after the election. There will only be a vacancy if she stands down. But when she argues that women might have made a difference to the performance of Lehman Brothers, or that a woman should always be in one of the top two positions in the Labour Party, she is putting a case and not preparing a leadership bid.

Mandelson's situation is more interesting. Tantalisingly for him as things stand, he is much the best-qualified member of the Cabinet to be Labour's next leader. Mandelson understands how to link tactics and strategy to policymaking, not an easy connection to make – as David Cameron is currently demonstrating. Mandelson also has the experience of government and recognises the weaknesses in the Conservative leadership. As a bonus, he understands the rhythms of the media fairly well, although he still makes a surprising number of gaffes.

Brown was indeed planning to announce during his party conference speech that he wanted to take part in televised debates with Cameron during the election. He had hoped to spring a surprise, to get momentum from the challenge. He still might go for it, but Mandelson gave the game away in advance by suggesting such a move was possible; quite a cock-up. On the whole, though, Mandelson's star shines brightly in an otherwise darkish sky.

In what context could he make his move towards the leadership? This is where the difficulties begin. When the new political season kicks off next month, he will be central to Brown's attempt at a comeback. Having made his decision that Labour's best bet is to buttress Brown, Mandelson would undermine his own credibility by knifing the Prime Minister, standing down as a peer, fighting a by-election and then taking part in a leadership contest as a newly-elected MP. Apart from anything else, there is no space between now and the election for such a time-consuming process, with the tottering Government on hold after a traumatic act of regicide as Mandelson becomes an MP in order then to become a candidate. I am exhausted outlining the sequence. It will not happen.

Nor would such a series of events enhance Mandelson's reputation. He has been at his best over the past year as the calm, good-humoured and influential elder statesman, slightly above the fray and yet at the heart of everything. Personally he has enjoyed the best media ever. All would change if he were to change from king-maker to king-seeker. If Labour loses the election, the focus will be on the next generation even if the party does not have a single credible younger candidate yet. In the event of a hung Parliament, there would be enough instability without adding to the frenzy as Mandelson moves to the Commons. The timing, context and sequencing make it impossible for Mandelson to become leader after the election.

If there is a leadership contest next summer neither Harman nor Mandelson will be Brown's successor; neither will even stand in a contest. The closest they will get to No 10 is their temporary occupancy during Brown's summer break. It is Peter's turn next week.

s.richards@independent.co.uk