Not even a trained arsonist could have imagined such spectacular pyrotechnics. This was Dominic Cummings’s wildest dreams come true. Revenge didn’t come sweeter than Boris Johnson having a breakdown during prime minister’s questions. And not just a minor hissy-fit, but a full-on disintegration of the psyche.

This was the Boris that the prime minister goes a long way to conceal. Normally we get to see the careful construct of the happy-go-lucky joker, but here he was stripped back to something much uglier: the primal rage of the narcissistic teenager who has been caught out and has no place left to hide. An anger made worse by the knowledge that, as so often, most of the damage was self-inflicted.

Even without the Electoral Commission having said it would be launching an inquiry into Johnson’s redecoration of Number 11 just an hour before PMQs began, there was little doubt where Keir Starmer’s attention would be focused. Not least because Dom had all but set the six questions up with his blog the previous week, in which he had broken the story about both the bodies piling up and the unorthodox way in which Boris had allegedly paid for his Downing Street refurbishment.

Starmer started with the bodies. Had the prime minister said “piling up the bodies” or something like that after a row about the second lockdown last October? Absolutely not, Johnson insisted. And anyone who said different was a liar. Fine, replied Keir. He was only checking because several people appeared to contradict him and it would be important at some stage to determine who was telling the truth. After all, it was an offence to mislead parliament.

The Labour leader then moved on to the decorations. The John Lewis furniture that Michael Gove’s wife, Sarah Vine, had, earlier on the Today programme, helpfully explained had needed to be chucked out because someone as important as Boris couldn’t be expected to live in a skip. With friends like Sarah … So who had paid the initial £56,000 invoice for the new soft furnishings?

Now Boris started ranting. “I’ve paid the bill personally,” he said. And it hurt. It was bad enough that he had been forced to take a major pay cut to be prime minister – how could anyone get by on £150K per year? – but it had never occurred to him that he would expected to pay for his own living arrangements. Parting with cash was for the little people. And if he had ever suspected for a minute he would have to fork out for a £10K sofa, he would never have let Carrie order one from the posh catalogue.

Most people he cross-examined generally just said “no comment” at thispoint, Starmer observed, before having another go. This time he tried multiple choice. Had it been the taxpayer, the Conservative party, a Tory donor or the prime minister who had paid the initial invoice? Again Boris avoided the question by repeating that he had ended up by paying and he couldn’t see what all the fuss was about. He might find that the Electoral Commission isn’t so easily fobbed off with him answering a different question from the one asked.

By now Johnson was in full rant, oblivious to everything but his own fury and a burning sense of injustice at being asked to pay for anything himself. Labour had spent £500K on doing up Downing Street, he said, so anything he had spent was chicken feed. He already seemed to have forgotten the £2.6m he spent on a brand-new media suite that he’s now too frightened to use in case people ask him any further awkward questions.

Starmer closed by listing the seven principles of the Nolan commission – selflessness, integrity, objectivity, accountability, openness, honesty and leadership – but Boris was too hysterical to take anything in. Instead, he got sweaty and just shouted about why he wasn’t being asked about the vaccine rollout and other things that were going well. He even threw in a lie about Labour not having voted for the Brexit deal, just for the hell of it. A few Tory backbenchers cried out “more, more”, but most had the decency to look embarrassed.

This was always how it was going to be. Just as Cummings had predicted when he went public with his dirt. It was never going to be the big things that brought Boris down. The public could tolerate any amount of untruths about Brexit and incompetence at the handling of the coronavirus in the first nine months of the pandemic. That was all priced into the Johnson public persona. The Careless Dr Feelgood.

It was always going to be Boris that did for Boris. The sense that the country’s priorities only took precedence when they happened to coincide with his own. And today we had seen that Johnson’s actual priorities lay in self-preservation. The refusal to say who had paid for the refurb. The personal briefings to newspaper editors trashing Dom. This had shown the real Boris. The nasty, self-serving Boris. The Boris for whom ordinary rules do not apply. The Boris he went out of his way to keep hidden.

This wouldn’t be the end of him. PMQs was too niche for that. But there was a feeling there had been a seismic shift for all those who had witnessed it. What had been seen could not be unseen. There is a crack in everything. That’s how the light gets in. The SNP’s Ian Blackford used his questions to ask whether Johnson considered himself to be a liar. Curiously, Boris didn’t answer. It was the closest he got to telling the truth throughout the session.