In 2002, Boris Johnson, then Member of Parliament for Henley, made a speech at the Mayor of Henley’s annual dinner. A Labour councillor present took against the political tone of the speech, and threw a bread roll at him.

As the then editor of this paper, I commissioned Boris to write a piece about the occasion. He is, among many things, an expert in the arts of rhetoric as developed in ancient Greece and Rome.

He began by describing the bread roll as it took off across the banqueting tables of Henley Town Hall. Leaving the roll in mid-air, he devoted the bulk of the column to whatever it was he was wanting to say about (so far as I remember) Tory policy. Only as the article drew to its close did he revert to the trajectory of the bread roll, identified by a witness as “a mini French baguette”.

It hit him, he reported, in the face. As he admitted when I asked him, Boris was consciously using an ancient rhetorical device. The fact that the roll took off, but then did not land, kept his readers in suspense.

Wanting to know what happened to the roll, we read the rest of the article with amusement and interest, waiting for the mini-baguette to find its mark.

Unlike Boris, I am no classical scholar, but I believe this technique is called digressio, and was practised by Cicero. Perversely, it achieves its main aim by diverting from it. As we consider the current excitement about whether Boris could ever lead his party, this concept of digressio may hold the key.

Let us use it ourselves. Let us start with the fact that at Oxford, Boris made a decision about where to channel his huge ambition. Born in America, he had the possibility, he thought, of being the president of the United States. But he also thought he could be the prime minister of Great Britain. Reckoning that he had more chance with the latter, he chose the road to Downing Street.

Now let us leave that decision hanging, mini-baguette-like, in the air, and consider the rest of the story. First there is Boris the Bullingdon blood who marries a beauty as soon as he goes down from Oxford. Then there is the young rapscallion Daily Telegraph reporter in Brussels, the first journalist to understand that “Europe” could be turned into a cracking story of continental bureaucrats taking advantage of this country.

Next follows the brilliant columnist, witty after-dinner speaker, novelist, Have I Got News For You guest, Don Juan and family man (yes, both), editor. All part of the digressio.

Then there is Boris Johnson MP, and for a brief period there is a real danger that our hero is straying from his own rhetorical device and returning too quickly for his own good to the real theme of his life.

Sure enough, Boris did not do very well in the House of Commons. He was not assiduous. His fame provoked jealousy. He was considered too bumptious or exotic (as, once upon a time, were Winston Churchill and Disraeli).

He encountered the disfavour of his party’s leadership, for lying to it. He began to look seedy. In 2005, David Cameron, a younger Etonian, became leader of the Conservative Party. Boris was getting nowhere. But then, in 2007, the Tories could not find themselves the right candidate to take on Ken Livingstone for the London mayoralty election the following year.

Suddenly, Boris saw his chance. He was selected, and then elected, thus becoming (as he remains) the only Tory since 1992 to have won any important political contest outright. Last year, he won again.

Last week, in Hyde Park, the mayor welcomed the Olympic torch with a speech of such gusto that the crowd chanted “Boris! Boris!”

This week, he was left hanging in the air for five minutes, stuck on a defective zip wire and waving two Union flags, but this only added lustre to his unique status.

Again, Boris has deployed the digressio. You cannot, in practice at least, be prime minister unless you are in the House of Commons: Boris is not, and cannot be until 2016 when his current term of mayoral office ends (though one would not put it past him to find a way of getting out earlier).

This looks like a disadvantage, but it isn’t. As conventional Conservative politicians are tangled in the tentacles of coalition and mired in the slough of economic despond, Boris is somewhere else.

Digressive, transgressive, subversive, Boris is in the “wrong” place at the right time. The crowd is loving it, and watches with increasing eagerness to see how he will return at last from the digressio to the main subject with which his adult life began.

Sensing this, Boris’s critics are getting as excited as his fans. Articles argue the impossibility of his being prime minister with a vehemence which shows their fear that it is all too possible.

You can sympathise with the critics’ anxiety. In the two-and-a-half-thousand-year-old argument about rhetoric, they are with Socrates (as rendered by Plato in his Gorgias). Socrates says that just as gymnastics and medicine are good for the body, so legislation and justice are good for the soul. Rhetoric, on the other hand, is bogus. Cookery, he says, is a sort of impersonated medicine and “Rhetoric is to justice what cookery is to medicine”.

Boris, to his enemies, is more rhetoric, the TV chef of modern politics, insouciantly rustling up “signature” dishes with ingredients prepared earlier by others. What does he stand for, they complain. What has he actually done? Is he serious? Equipped with the appropriate learning, Boris would riposte with the arguments of Aristotle, who sees rhetoric as a true and necessary art.

His supporters insist that democratic leadership can only succeed if it speaks in a way which persuades people to listen, and if the speaker is himself, as a character, convincing. You could hardly think of two more different characters than Margaret Thatcher and Boris Johnson, but they share this one thing — this gift for being noticed, for compelling attention, for making voters think again.

Of whom else, in politics just now, could this be said? Under the leadership of David Cameron, the Conservatives have devoted themselves to modernising. Much of this was necessary, but modernising itself now feels rather out-of-date, rather Millennium Dome. As you could tell from the London Olympic opening ceremony, we now have a post-modern public culture.

We are ironical, eclectic, genre-subverting, fusion-cooking, mixing up Chelsea Pensioners and lesbian kisses. We are high-brow and low-brow at the same time.

The only politician who “gets” any of this is Boris. He can mix Virgil and James Bond, a posh accent and street cred, conservative politics and a liberal spirit. Cameron is the moderniser, but Boris is the post-moderniser.

To the many — possibly including myself — who would prefer our politics plainer, all this may seem footling. What has it got to do with righting our ghastly economic wrongs? Very little, perhaps. Boris Johnson’s instinctive, freedom-loving, anti-statist optimism is attractive, but certainly does not amount to a policy.

Besides, the fashion for writing off Cameron has gone far further than the facts warrant. It could well be that Boris’s great digressio ends with no more than a bread roll in his face. All I would say, though, is that conventional politics is now failing more comprehensively than at any time since the 1930s, and that Boris Johnson is the only unconventional politician in the field.

The Daily Telegraph