“The hour is darkest before dawn,” Boris Johnson ventured in one of those faux-Churchillian opening lines that he knows are guaranteed to warm the hardest of Tory hearts.

At Saturday’s first hustings in the final round of the Conservative party leadership contest, Johnson was referring to Brexit, but it was also the closest he came to addressing what moderator Iain Dale called “the question on everbody’s lips”. “They want to know why the police were called to your house at one o’clock?” Dale said.

“Iain, listen, I think what people have come here today for is not that kind of thing,” Johnson replied.

However successfully Johnson stuck to that line, this is not how it was supposed to be. When the final two leadership contenders were announced, it had appeared these hustings had been engineered by Johnson’s supporters as 16 non-events, the ultimate mismatch between headline act and lacklustre support band; the blond leading the bland. In the event, in Birmingham on Saturday, Johnson was inevitably confronted with the pressing subject he had been at pains to keep hidden from the public eye: his personal suitability for the highest office.

His opponent Jeremy Hunt’s best hope had always appeared to be that Johnson would in the course of a fortnight locate some unexplored way to self-destruct and keep their tour interesting. Johnson’s best efforts at restraint had given out before he made it to the first gig.

A domestic argument in the household of almost any other prime ministerial candidate might not be front page news, but here it spoke to wider concerns about Johnson’s conduct. In a leadership campaign in which he invited precisely six questions by the critical media and answered not one of them, he clearly believed he could make it to No 10 with just the tricks that have served him well thus far: mussing his hair and half-smiling at his shoes, a couple of mumbled jokes and a smattering of Latin.

The format of this first event – one candidate appearing after the other meant there was no possibility of the rivals confronting each other directly. Hunt was probably even more grateful for that than Johnson. Having made a few decent jokes of his own – including how he had rejected #huntymchuntface as a campaign hashtag – Hunt stressed pointedly how “if we send the wrong person to negotiate in Europe catastrophe awaits”.

The foreign secretary’s favourite adjective to describe his plans for the economy and the country should he become prime minister is “turbo-charged”. In delivery and demeanour, however, he is more of a two-stroke lawnmower, puttering along steadily, thinking and speaking in careful straight lines. As an aggressor he exhumes nostalgic thoughts of former chancellor Geoffrey Howe’s dead sheep. It is hard to imagine a politician – even Theresa May with her well-known allergies to spontaneity – who would not have essayed at least an aside about the front pages that had been the starting pistol to this campaign. Hunt declined to do so.

Dale eventually gave up as well. As the publisher of the book that revealed Michael Gove’s cocaine use, he has already played a decisive role in this contest. He tried to press Johnson on the press reports. “If the police are called to your home, it makes it everybody’s business…?”

“That’s fair,” Johnson replied. “People are entitled to ask me about my character.” And then he proceeded to talk about anything but.

Facebook Twitter Pinterest Boris Johnson in Birmingham yesterday. Photograph: Christopher Furlong/Getty Images

“Does a person’s private life have any bearing on their ability to deliver?” Dale tried again. Johnson talked about how as London mayor he had cut the city’s murder rate. About his role in the Olympics.

On his fifth effort to ask the same question, Dale was shouted down by the Birmingham audience. “Don’t boo the great man,” Johnson suggested to his crowd, in his Wooster-like take on Trump’s rabble-rousing against fake news. Johnson’s greatest weapon up until now – a trait he shares with both Donald Trump and Nigel Farage – is that he is unembarrassable. Charges of hypocrisy or lapses in judgment or blatant untruths are not only laughed off but repurposed as evidence of his “character”. His deflections are largely ignored by this particular electorate.

The notion of the Tory party as the bastion of law and order and family values disappeared in 1992 with David Mellor’s Chelsea shirt. It is now the party that would, on the basis of last week’s polling, accept the break-up of the union and the collapse of the economy just to “secure Brexit”.

In collective character, on social media at least, it sounds indistinguishable from those Ukip town hall gatherings that Farage worked so hard to assemble in the years before the referendum. Talking to the early arrivals in Birmingham, it was clear there was only one subject on their minds: Brexit. A group of four women from Herefordshire, each with 50 years’ Conservative membership behind them, told me they could not give a hoot about Johnson’s private life. “It’s a storm in a red wine glass. If he’d spilt anything on my sofa, I’d have been slamming doors too.”

Some of the younger Tories I speak to dismiss the story as a simple smear. Samuel Tapper, 20, a councillor for Chasetown in Lichfield, who recently won a once safe Labour seat, said: “I think the incident overnight was at best speculation. We don’t know what happened. We shouldn’t start taking stuff that we have heard as facts.”

Izzi Seccombe, leader of Warwickshire council, who began supporting Rory Stewart, then Gove, was among the few who thought Johnson’s character might be an issue. “What are the characteristics of the choices you make in life? I think that’s important. It is disappointing it came out now rather than two days ago.”

The phrase that came most readily to mind, talking to these members, however, was that campaign assertion by the US’s 45th president that he could “stand in the middle of Fifth Avenue and shoot somebody and [not] lose any voters”. Johnson, over the coming fortnight, is set to test the tribal spirit of that group for which the word “base” sounds ever-more appropriate. It is unlikely in our strange polarised political times there is any character flaw even in Johnson’s make-up that will derail him.

With the right energy and commitment we will pitchfork this incubus off our backs Boris Johnson

The reported angry words of his girlfriend Carrie Symonds, “You don’t care for anything because you’re spoilt. You have no care for money or anything,” might well have sounded like a solid basis for policy arguments in a part of this audience.

When the candidates got on to the subject of Brexit – that other domestic row conducted within the earshot of concerned neighbours, in which one aggrieved party was yelling “just leave” and the other refusing to go – both laid out their well-worn “strategies”. Johnson talked, in his usual mocking tones, about how he would be proceeding with “great tact and sensitivity”.

He still wants to make the negotiation sound a piece of cake. “All I can say, I am utterly convinced that with the right energy and the right commitment common sense will prevail…” he said. “We will pitchfork this incubus off our backs.”

In the absence of credible argument, most of Johnson’s cheerleaders return to the idea that he will offer the poetry of blind optimism where others come armed only with prosaic realism and facts. That he will perform for the country the role he has long performed at Tory conferences: he will stamp clumsy potato print colour on a folder of monochrome debate.

Before the end, Johnson was looking at his watch. “Are you bored?” Dale wondered, before having one last go: “What’s the biggest personal crisis you have ever faced?” “London riots,” Johnson said.

“I was on holiday. It was an absolute nightmare.”