Tony Benn in his pomp used to rebuke journalists for failing to realise that "policies, not personalities" were what mattered. The less-than-subtle suggestion was that serious men of ideas - possibly named Benn - were not to be detained or distracted by froth, gossip and human trivia. Unlike, it went without saying, certain eternally puerile media lackeys.

It all made Benn sound impressively high-minded. It also made him sound ridiculous. The stricture was the equivalent of those defunct schools of literary criticism given to insisting that a writer's life and intentions are of no account and that only the "text" matters. Among others things, it overlooked the obvious: for voters, children that they are, a politician's personality counts for a lot.

There is nothing to prevent a vain, vindictive neurotic from coming up with a plan to transform health services, of course. Some people would even insert the name Nye Bevan in that sentence. There is no rule, either, that says a Prime Minister cannot be both great and off his (or her) trolley. You can make your own list for the quiz. But those who vote still hanker for the idea that a politician, if worth the bother, will embody certain virtues.

Not lying too obviously or too often will get you a long way. Not screwing up on a weekly basis is useful. Some favour the compassionate type, some the inspirational. Some go for youth, some for experience. Some, inexplicably, prefer a politician who is "one of us". Toughness, boldness and courage have their fans. Then there is the indefinable quality we call leadership. Roll that lot together and the election is in the bag.

The list omits two facts. One is that politicians are well aware of what we think we like. They try to supply it. Since very few of us actually know the candidate personally, however, hired hands will make good money attempting to manufacture the sure-fire political personality for all seasons. The second omission is obvious: you can't buy charismatic leadership in a flat pack from Politicians R Us.

The Labour Party - it was its turn - has just learned as much. Not so many months ago it seemed self-evident that Gordon Brown should succeed Tony Blair, and that Wendy Alexander should be elevated to the Scottish leadership. Both were nodded through by acclamation, if you can picture it. No-one wasted breath or effort opposing the inevitable. The pair were, in the proper sense, unrivalled. Good plan.

This morning it is no longer a joke to ask whether one or the other is up to the job, or whether either can last. They are in big, enduring trouble. Not because of a lack of brains - quite the opposite. Not because any personal wrong-doing has been attached to their names. Not because - certainly not because - there are plausible candidates waiting to take their jobs. Instead, there is merely the corrosive sense that they just can't hack it. They are lacking as leaders.

Quite how a run of bad luck equates to intractable personality failures is never explained. Not so long ago, after all, Mr Brown was earning good reviews for decisive action in the face of floods and sick livestock. Ms Alexander was believed, briefly at least, to be bringing clarity and purpose to a demoralised and resentful Scottish party. Now the secret (or not so secret) vice of British political life has them fighting for their lives. Worse, it has voters asking if these are the leaders we need and demand.

The question is a hard one for the embattled duo to answer. The real trouble with personality politics is that it leaves no room for party, for support or solidarity. When you isolate a chosen individual from a mass movement, when you specify that only the star can be centre-stage, you merely paint the target. Name me the trade union leaders who this week stepped forward to say they were sending their support, and large cheques, to Gordon.

It is no coincidence that party funding and issues of personal leadership have come together for Brown and Alexander. One is the adjunct of the other, these days. In the latter case, the money raised, down to a Jersey businessman's "impermissible" £950, was intended for the promotion of Wendy, pure and simple. In London, equally, the frantic and squalid attempts to plug holes in Labour's finances - caused by previous squalid and frantic efforts - arose from the need to match the Tories in selling the leader and his "personality" to the public.

Now, ironically enough, the packaged figureheads will have to emerge as real leaders if they are to survive with their credibility, their dignity and their ambitions intact. Tricky.

Sacrificing a few bit-players looks like an attempt to shift the blame. Airing every piece of dirty laundry without being asked - page one in the Alastair Campbell crisis-management handbook - looks calculated, because it is. The full grovelling apology (Ms Alexander made her contribution to the genre yesterday) invites a simple riposte. If you knew these things were heinous, why did you allow them? You were supposed to be in charge.

Taking charge is what a leader does, but what does it mean? Taking control of every detail? Brown's obsessive efforts in that direction are now part of the indictment. Strangely enough, he micromanaged at every level yet knew nothing about any illegality. Truly? Deny that plausibly, someone is liable to say. They will say it to Alexander, too.

In both cases, leadership has been reduced to the most base common denominator. Why are they struggling to close down their crises? Because, ironically enough, they are both freaks when it comes to personal control. They have confused leadership with handing out orders, with (it is alleged) pushing people around, with having their own way. But as students of political personalities tend to observe, these are signs of weakness, not strength, of brittleness, not durability.

If that's the case, Mr Brown and Ms Alexander will need to change their ways in order to survive. Indeed, it was claimed, funnily enough, that both were embarked on the selfsame process before obscure donors reversed nature and began to draw blood. Yet the tactic, for a tactic it is, only makes matters worse. It's called pretending to be someone you are not.

The existence of an actual, living Labour Party might have helped the pair, but that entity has been reformed out of existence, generally with the enthusiastic support of the Prime Minister and Donald Dewar's latest successor. Stricter political funding laws would have made a difference, but we know now what lies behind all the noble rhetoric of transparency and honesty.

The fact is that the parties, Labour in particular, set about subverting the 2002 reforms the instant they were introduced.

The British party of government undermined its own laws, in London and in Scotland, by subterfuge and deceit. That is the real, lasting charge against anyone who claims leadership. Not who you are, but what you do. Not what you do, but what you fail to do. Not the spotless personality capable of inspiring belief, but the person capable of cleaning out the muck when things are beyond belief.

Does either have what it takes? I doubt it. Think first and last of what made them.