Tony Benn is, I find, wrong about most things, but the thing he was most wrong about was this dictum: the least important aspect of politics was personalities, he said, the next least important was policies, and the only one that really mattered was values. No, no, and no. 'Values' is one of those words that sound tremendous but actually mean whatever we want them to mean. Are we in favour of prosperity? Low unemployment? Do we like the notion of opportunity for everyone? Is peace preferable to war? Of course. They're all values. As a means of dealing with the problems of taxation, of social organisation and of national defence they are next to useless, the equivalent of a nuclear physicist facing a knotty problem and asking himself what Mother would have done.

Here are values in action, and it's an example Benn often gives. Mr James Dyson, inventor of the Dyson vacuum cleaner, has moved his factory from England to the Far East, with the loss of several hundred jobs. "For profit!" as Benn says, the implication being that a person of values would eschew profit in order to preserve jobs.

But that wasn't the problem facing Mr Dyson. His competitors were already making their vacuum cleaners in the Far East, and consequently selling them at, say, £50 less each than the ones he made in the UK. What was he to do? Struggle on in a harsh competitive market, trying to sell what would inevitably appear to be overpriced machines? If he did he would quickly go out of business, and the workers would be unemployed anyway. If he kept his operation here, he would inevitably be asking his customers for a £50 donation to the Distressed Vacuum Cleaner Manufacturers' Benevolent Fund — a worthy cause no doubt, but not one most people would stump up for. They'd buy an Electrolux, or a Hoover. The middle class people who applaud this line at Benn's stage appearances are almost certainly those who look up Which? magazine and choose a Miele as best buy without caring where it's made.

(Attending a Benn performance at the Royal Festival Hall once, I interviewed a middle–aged couple during the interval. "We like Tony Benn," said the husband. "Yes, we think he speaks for people like us," agreed the wife. I asked if they had always been revolutionary socialists, and they looked appalled. "Oh, no, we generally vote Conservative," they said.)

So as a means of tackling that moral conundrum, values are next to useless. Your values might stop you wanting to go to war in Iraq. Would those same values support keeping Saddam Hussein in power? I assume your values are against seeing people torn to shreds by car bombs. But do they stop short of allowing suspected terrorists to be jailed without trial? Prison without trial or limbless children? Do your values help there?

Policies are a slightly better guide. In the late 1970s the Labour left toyed with the idea of a siege economy as a means of rescuing Britain. It had nothing to do with values, and everything to do with a theory: banning imports would preserve British jobs. It would also have put us on a straight path to becoming the Cambodia of the West, but, thank goodness, it was never tried.

One reason it was never tried was, as it happens, personalities — which are, in my view, much the most important element in politics. Suppose Ted Heath had decided to retire gracefully from the Tory leadership when he lost the second general election of 1974. His replacement would almost certainly have been Willie Whitelaw, a consensual moderate, and as far from the policies of Margaret Thatcher as it was possible for another Tory to be. But Heath was a stubborn old cuss, and saw no–one fit to replace him, so he hung on into 1975. Even then Whitelaw would have won if Heath had resigned, but he didn't; he issued a 'back me or sack me' demand instead. Whitelaw, being a gentleman from the old school (Harrow) could not stand against his commanding officer. The few months between the election and Heath's demarche allowed Margaret Thatcher the chance to shine in the Finance Bill committee and to attract the admiring attention of Tory back–benchers…. The rest is history, but history based entirely on personality. If a butterfly flapping its wings in Japan can create a hurricane in Florida, how much more influential is a character trait in a powerful politician?

Tony Blair's personality includes a need to be liked. This can be fatal in a politician, since politics is a matter of choosing your enemies carefully. Civil service grandees can be near despair when a foreign leader arrives in Downing Street, since Blair can scarcely prevent himself from making more concessions even than the visitor has asked for. The recent U–turn over a referendum on the new European constitution can be tracked back to Blair's anguished need to choose between the Murdoch press and his chums in the chancelleries of Europe.

Margaret Thatcher had no such needs. She relished combat and gloried in opposition. If other EU leaders weren't reviling her, she wondered what she was doing wrong. Once she had decided she had no time for Sir Geoffrey Howe she began a programme of humiliating him — taking away his grace and favour house, even though it was his main home, then attacking him in Cabinet for the failings of junior ministers over whom he had no control. If she had been more ameliorative — more of a Blair, in fact — he would never have made his lethal resignation speech. Perhaps he wouldn't have resigned in the first place. She would have stayed in office and, who knows, Neil Kinnock could have won in 1992.

Forget policies, and most of all forget values. It's personalities that matter, and in the end decide how much tax we pay, where our children go to school, and whether the nation goes to war.