Let’s begin with the straightforward part: any incident in which a woman is heard screaming in her home, and shouting “Get off me!” at a man, instantly becomes a matter not only of public interest but public responsibility.

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The precise motives of the neighbours who called the police on Thursday night to report the row between Boris Johnson and his partner, Carrie Symonds – and also alerted the Guardian – should be a matter of near total indifference. So what if they were “remoaners”, or Tory haters, or vacationing ministers in the Venezuelan government? Would it really have been better if they had let it be? Allowed whatever was happening to run its course, on the old, deplorable basis that it is intrinsically wrong to intervene in a “lovers’ tiff”?

None of us yet knows precisely what took place between Johnson and Symonds. But – forgive my frustration – that’s the point. The only defensible response of a neighbour in such circumstances was to contact the police.

I have argued in the past that Johnson’s turbulent private life is a poor basis on which to attack him. One of the great improvements in British political culture in recent decades has been the decline of moral puritanism: after the fiasco of John Major’s “back to basics” strategy, a new and sensible consensus emerged that sexuality, infidelity and marital status are no long fair game in political conflict. But that shift does not represent a blank cheque. Yes, the police left Symonds’ flat satisfied that “there were no offences or concerns apparent to officers”. But the mere fact that the man poised to become prime minister in a few weeks was involved in an alarming altercation in which a neighbour felt it necessary to call police is self-evidently a legitimate matter for public inquiry.

Broadcaster Iain Dale was quite right to press Johnson on the matter at the Conservative leadership hustings in Birmingham on Saturday. Others should now do the same. We have absolutely no right to know more about, say, the petty private details of Johnson’s prospective divorce from his second wife, or the state of his relationships with his children. We have every right to ask why his partner was screaming on Thursday night and telling him to “get off” her. The line between private and public was clearly breached, and it is time that some of Johnson’s more fanatical supporters acknowledged this basic moral distinction.

And there is another, more nuanced dimension to this grisly episode. The person who, so to speak, led us to the door of Symonds’ flat in Camberwell is none other than Johnson himself. His repeated insistence in Birmingham that people didn’t “want to hear about that kind of thing” rang hollow precisely because – more than any other contemporary British politician – he has tried to turn public life into a game of personality, in which wit, confidence, charm and personal presence eclipse policy and substance. This is the proposition upon which his bid for the top job is based: that character is all. It is hardly surprising, then, that his character is now being examined as never before.

One should perhaps more accurately say “character”. For the personality that Johnson has presented to the world is a confection, a stage act with roots in his true nature but with many affectations and contrivances. He is, one should never forget, “Al” (for Alexander) to his loved ones. “Boris” is a persona: it is his populist Conservative version of Ziggy Stardust, The Rock or Borat. It is a means to an end – and a potent one.

Over the years, the character of “Boris” has proved to be a vehicle for some pretty horrible rhetoric: most recently, his declaration that a Muslim woman wearing the niqab resembled “a bank robber” and that it was “absolutely ridiculous that people should choose to go around looking like letterboxes”. He has called homosexual men “bum boys”. He has – unbelievably – written about “piccaninnies” with “watermelon smiles”.

His trick seems to be to scuttle behind the increasingly tattered defence that he is only trying to be funny, that his remarks have been taken “out of context”, that he is the victim of our old friend, political correctness gone mad.

To his liberal audience, he says: lighten up. To his hardcore rightwing fans, he winks like Donald Trump, as if to say: I’m on your side, just so you know.

Indeed, it has become something close to a parlour game in the political and media class to chatter about “the two Borises” and wonder which is authentic. Which will we get in No 10: nice Dr Jekyll, the supposedly liberal Johnson who won the London mayoralty by posturing as a friend of immigration, diversity and pluralism? Or nasty Mr Hyde: the burqa-bashing populist who has led the charge for Brexit, says “fuck business” (and, presumably, the jobs that go with it) and treated the case of an imprisoned British-Iranian woman with indefensible sloppiness?

I find this parlour game – this reduction of British politics to a low-rent Churchillian soap opera – unforgivable. No less outrageous is the undiminished determination of the Tory tribe to give this untrustworthy charlatan the keys to No 10. As Dale pressed him on Saturday, the audience of true believers booed. They (like Johnson) regard difficult questions as an impertinence: it is no accident that their hero looked so furious in the BBC candidates’ debate last week, or that he has yet to agree to take part in the planned Sky News debate with Jeremy Hunt.

Trump once said that he could “shoot somebody” in the “middle of Fifth Avenue” and not lose any votes on the road to the Republican presidential nomination. Johnson apparently enjoys his own version of this immunity within the Tory stockade.

Why do they cling to him so? Because he incarnates hard Brexit, which for the Conservative movement – once described, without irony, as the “natural party of government” – is now a religion rather than a hugely complex, commercial and institutional process. So sacred has this single objective become that – according to a YouGov poll last week – most Tory members would be willing for their party to be “destroyed” in order to accomplish the holy task of Brexit. Once the most electorally successful force in the free world, they have become a death cult. Johnson, the L Ron Hubbard of the Church of Brexitology, reassures them that leaving the EU is anything but complex. In fact, it could not be easier. It just requires confidence, brio, va-va-voom. In other words: him.

Which brings us back to Thursday night, a woman’s screams and a fracas that may have much to tell us about the man set to become prime minister in little more than a month. If it’s all about him, then we have a right to know everything about him. So many questions still to ask. All eyes on you, Mr Johnson.

• Matthew d’Ancona is a Guardian columnist