Boris is booming. The Sunday papers seem to be wall-to-wall Boris: see our Newslinks for the way he dominates the front pages.

But for some weeks, I have known the Boris bubble was swelling to barely comprehensible, and to some people highly alarming, dimensions.

As his earliest and most frivolous biographer, I can detect, with the sensitivity of a trained parasite, the early signs of a Boris boom, for there is a correlation with the growing number of requests I get to write and talk about him.

What a scene-stealer the man is. A few deft touches on the volume knob – a readiness to stretch the boundaries of good taste just a sixteenth of an inch beyond what respectable opinion will tolerate – and pow, there he is, obliterating for an hour or two the build-up to the Queen’s Speech.

Look how the Member for Uxbridge and South Ruislip did it in his interview in this morning’s Sunday Telegraph:

“The whole thing began with the Roman Empire… I wrote a book on this subject, and I think it’s probably right. The truth is that the history of the last couple of thousand years has been broadly repeated attempts by various people or institutions – in a Freudian way – to rediscover the lost childhood of Europe, this golden age of peace and prosperity under the Romans, by trying to unify it. Napoleon, Hitler, various people tried this out, and it ends tragically…

“The EU is an attempt to do this by different methods. But fundamentally what it is lacking is the eternal problem, which is that there is no underlying loyalty to the idea of Europe. There is no single authority that anybody respects or understands. That is causing this massive democratic void.”

While Mr Johnson is not arguing that the bureaucrats of Brussels are Nazis attempting to bring back Hitler’s Reich, his comparison is startling. Clearly, he sees parallels between the choices that confronted his beloved Churchill, and Britain, during the Second World War and the decision facing voters next month.

“This is a chance for the British people to be the heroes of Europe and to act as a voice of moderation and common sense, and to stop something getting in my view out of control,” he says. 

A six-letter name beginning with H and off the story goes. In no time at all, his fellow Balliol person, Yvette Cooper, is condemning him for playing “a nasty, nasty game”, while on his own side (though on the opposite side in the European debate) Nicholas Soames describes him on Twitter as “The unchallenged master of the self-inflicted wound”, hash-tag #sansjudgementsanscredibility.

In a coruscating piece for the latest London Review of Books, entitled “Nigels against the World”, Ferdinand Mount ridicules a number of the Leavers. He has Michael Gove “looking more than ever like a gleeful hamster on steroids”, while Matt Ridley is dismissed for his “flamboyant optimism, first seen in action when he was the chairman of Northern Rock”.

But the first Leaver whom Mount accuses, in a couple of detailed paragraphs, of having not much clue “about what is to happen afterwards”, is Boris: “Johnson in particular changes his ideas once a fortnight.”

The referendum is becoming, or perhaps always was, a struggle between two quite different mentalities. This is how, in a democracy, people discover which side of the argument they are on.

The Remainers are led by Establishment Man (or Woman, but in its purest form, the male version still predominates). He is a civilised person, who under normal conditions – i.e. when he is running the show – has a good sense of humour.

But he is profoundly shocked by the irresponsibility of the Leavers, with their apparent belief that one can just make things up as one goes along, and needn’t worry what the consequences might be either for oneself or for other countries.

On the other side, we find the Free Spirits, or mavericks, who see life as a glorious adventure, in which one’s liberty should be shackled by as few rules, regulations, treaties, obligations and inhibitions as possible.

David Cameron is a perfect example of Establishment Man. He stands (as Gordon Brown once did) for Prudence; won the last general election by appealing to our cautious preference for the devil we know; hopes to win the referendum by making the same case.

The Establishment decided during the prime ministership of Harold Macmillan (1957-63) that the prudent thing to do, or at any rate the least bad, was to join the Common Market, as it was then known. Cameron is Macmillan’s successor: a progressive, liberal, pragmatic, Anglican Conservative, whose upper-class connections conceal from most observers how ruthlessly professional he is. Ferdinand Mount is Cameron’s mother’s first cousin.

Boris, one need hardly add, is the most famous Free Spirit in politics. He takes risks, tells jokes, gets stuck on zip wires, makes disreputable references to Hitler.

Because he is unpredictable, he is amusing to watch. One never quite knows what he will say or do next. There are occasions when he himself does not know what he will say or do next, but there is also a vein of deep calculation behind his antics.

He is now engaged in a vast popularity contest, of a kind he has specialised in since the age of 16. It is possible that the more indignant the Establishment becomes, the more popular he will grow, so that his claims to be Captain of the School, or President of the Union, or Editor of the Spectator, or Mayor of London, or Leader of the Conservative Party, can no longer be denied.

But it is also conceivable that the Boris balloon, having swelled to unimaginable size, will quite suddenly go pop, leaving behind a few shreds of brightly coloured rubber.