The Johnson world view is quite a cocktail, golf club opinions on a champagne base: denunciation of "the maniac Livingstone" for congestion charges, advocacy of wholesale public-sector sackings, approval of the Iraq war, opposition to the minimum wage, endorsement of George W Bush as a crusader against the Kyoto Treaty.

The aspiring candidate, however, has just proclaimed the total opposites of almost all of them.

A list of Johnson's new opinions facing a column of his earlier clean-contrary stands, once put into circulation by the Livingstone camp early in the campaign, will concentrate minds quite as wonderfully.

Johnson is a scatter-gun mouth, hopelessly frail in liberal, multi-racial London over a sustained election.

He matters rather as a symbol which might become a trend.

A regular TV presence on shows like Have I Got News for You has familiarised that loud and carrying voice, loud and carrying manner and attention deficit syndrome.

Like a drunken dolphin thrashing about and being measured by the spray, he has achieved celebrity. And celebrity rules.

Too high a proportion of the contemporary public, as measured by the tyrannical figure-counts directing TV quality downward, is besotted by people of negligible merit, chat folk, flashy presences without quality of mind, breadth or depth of interest.

Emotionally-fraught football commentator, smirking lady cook, booming anecdotalist, unpleasing racing pundit, newsreader, weatherman, pretty well any foot-soldier in the great chorus of Soap Opera, is a celebrity.

We used to have "personalities" – rather forlorn they seem now – Gilbert Harding, Isobel Barnet – people in recurrent private crisis clinging to public sympathy, they needed us.

Today, we have new improved celebrities, too many of them masterful, peremptory and cocksure. This lot, heroically paid and the running pre-occupation of an obsessive press, are as much a social elect as any landowning aristocracy, and people cling to them.

As long as it stays like that with the celebrity doing nothing worse than enjoying the attention and the money, or grieving about world poverty on camera, who can object? This is his long straw and he is enjoying it. Where we start worrying is the point at which the celebrity wanders into politics.

The opening is there to be taken. For the general run of politicians has been a desert of the uninteresting.

At best managerialists, too often film extras, they have become public ghosts.

The Leadership Principle has not helped. Big characters do not make the Cabinet. Prim Hilary Benn, pursing lips and compressing fingers; ex-Whips Office steady Jacqueline Smith, droning Des Browne: note the dazzle of pre-set concrete. And dear God, how can anyone possibly identify with Jack Straw?

This being the case, when some swaggering talk-show chatterbox offers himself to a struggling party, with fast lane prospects, the way will be open.

It happens in the US of course.

A soap actor, Fred Thompson already once in the Senate, has entered the Republican presidential primaries. The soft-shoe dancer, George Murphy became a Senator. The Austrian muscleman, Arnold Schwarzenegger, governs California, Ronald Reagan was President. What more can you say?

I met Reagan once at a get-together with Daily Telegraph leader writers. I remember a pleasant, courteous man, very like his TV image, and he was naturally cautious and bland in what he said.

But I remember, too, one opinion which sent the rugged Tories of the paper's old guard away shaking their heads. Someone raised South Africa and apartheid.

Reagan thought things were improving. Hadn't there been liberal moves recently? "Look at these new areas where the black people are governing themselves."

He meant the Bantustans, Lesotho, Botswana and the like, designed to keep black citizens outside metropolitan South Africa. It was a pretty crude and obvious fix.

But Reagan, hired by rich men as charisma, didn't begin to understand. He was there because dull-minded voters recognised the face, and
liked it. A gentle, lazy soul, he was utterly dependent on what his advisers told him.

Celebrity candidacy has not prospered yet in Britain. The dreadful Jimmy Edwards stood as a Tory and lost. Commander Kerans, briefly
a highly-publicised naval hero in China 50 years ago, was for one parliament a silent Tory MP. Martin Bell, a respected TV journalist, was elected as an independent after a scandal but never quite clicked.

But there was too, remember, Robert Kilroy-Silk from day-time TV who carried a cache of UKIP Europhobes into the European Parliament.

The way he then behaved, though happily, it did for him, serves as a warning. He demanded instantly to be made leader of a party he had just joined, before setting contemptuously about its leading figures and fizzling blissfully away. That sort of Napoleonic mania is natural in a celebrity.

Let's discount some people. Alan Titchmarsh would be as good as gold and ask pertinent questions of Defra Ministers.

But the big empty egos? Imagine glutinous Jonathan Ross with power, or Adam Hart-Davis or – let's hide behind the sofa – Marco Pierre White? Let's treat Bojo as an inoculation.

Edward Pearce is a political commentator and historian who lives near York