John Rentoul: Politics is not so full of personality that we can afford to lose more

She was a one-off, as the Prime Minister observed in his statement on Friday. It was the kind of cliché he had used before, at the 1998 Labour Party conference, when he listed his Government's achievements, ending with the Good Friday Agreement. "It took our one and only Mo, of course," he ad libbed, prompting applause that snowballed until the whole of the Winter Gardens rose to its feet, roaring. She was certainly a larger-than-life character; with her passing, and that of Robin Cook, politics seems a duller business.

It is not as if British politics is so densely populated by vivid personalities that it can afford a further thinning or homogenisation. There will always be complaints about how politicians today are pale shadows of the giants of yesteryear, just as people always claim that when they were children no one locked their front doors and we were always in and out of each other's houses.

Yet the ascendancy of Tony Blair did seem to represent the ultimate in the depersonalisation of politics. He is a politician of such self-discipline, such studied ordinariness and such consummate professionalism that almost all personality has been suppressed or smoothed over. Having written a book about him, I can testify that the most eccentric thing about him is the lack of any eccentricity whatsoever.

So here is an interesting question for the growing number of sixth-formers who, we learnt last week, are taking politics at A-level. Did the advent of Blair's style of personality-light leadership mark a permanent change in politics, or was it a temporary response to Labour's crisis of the 1980s and 1990s? Candidates would be expected to discuss whether, in an age of faster, more intrusive media, distinctive personality traits too quickly become political liabilities. Or was it simply that, traumatised by four consecutive election defeats, Labour's modernisers took defensive politics to its risk-averse conclusion? Marks would be awarded for mentioning John Major and Bill Clinton. Extra marks would be obtained by explaining that Major, a colourless character, was chosen as leader precisely because he offended the smallest number of his fellow Conservative MPs. Or by pointing out that Clinton managed to secure the presidency and win re-election, despite being a large and disordered character.

On this point, candidates would impress the examiner by citing The Survivor, John F Harris's superb study of Clinton's time in the White House. Its cool narrative shows clearly how the disorganisation and policy zigzags of the Clinton administration were not the product of inexperience, or forced on it by the opposition, but reflected directly the indecision of the President himself.

As an advanced extended option, to be marked by Lord Adonis personally, candidates could expound on how a larger-than-life personality in the post-Blair era might be a way in which politicians could recover a sliver of trustworthiness. One of the reasons why people like politicians such as Mo Mowlam or Denis Healey - even while recognising their weaknesses as national leaders - is because their oddity is evidence of their authenticity. Blair has few such defences to fall back on. When his integrity was questioned over Iraq, there was no persona into which he could retreat, of which people would say: "He got it wrong, but at least he is genuine." He tended to come across as a barrister making a case, and his passion seemed to be a means to an end.

Candidates could go on to explore the implications for the future leaderships of both the Labour and Conservative parties. Because Blair is widely seen as an artificial phenomenon, cloned in a tank by doctors Mandelson and Campbell, it is assumed that, in the competition to succeed him, a more rooted sense of personality would be an advantage.

Gordon Brown's character has a distinctive flavour by virtue of his Scottishness - like John Smith he has proved adept at exploiting the bank-manager quality of solidity implied by a softly rolled r. But beyond that, he is firmly of the buttoned-up school of self-suppression. The wit and sense of mischief sometimes on display in private are rarely seen in public.

It is the Conservative Party, however, that has the sharper dilemma. In Kenneth Clarke, it has one of the few really idiosyncratic characters in British politics. But his views on Europe make him intolerable to most of the Tory party membership - although that in itself should be an excellent reason for choosing him: it would be proof that the party had left dogmatism behind.

Hence the growing attractions of a joint leadership ticket, using David Cameron, the 38-year-old shadow education secretary to balance the perception of Clarke as yesterday's man. But much of the summer flurry of leadership jostling has been about securing positions of influence in a David Davis Shadow Cabinet or beyond. Davis remains the runaway favourite. And he is a man with, as yet, a biography rather than a personality.

Finally, however, the most astute students of politics - the ones who will in future be awarded As in all their modules - will point out that idiosyncrasies in politicians are often, at least in part, contrived. Mo Mowlam's loud informality was a bit of an act. What matters is not so much having a distinctive personality, but having the right image for the moment, and the intelligence and quickness behind it. What was most interesting about the Prime Minister's tribute to Mo Mowlam last week was his praise of her political (for which read emotional) intelligence: "Behind that extraordinary front presented to the world was one of the shrewdest political minds I ever encountered. She was a natural politician, could read a situation and analyse and assess it as fast as anyone."

That is the skill that unites successful politicians, from Margaret Thatcher to Bill Clinton, from Mo Mowlam to Tony Blair himself, regardless of how colourful - or colourless - their front.