A British politician never lies to Parliament. He or she may exaggerate, omit, or be economical with the truth; they may even slip, as Winston Churchill once did, into “terminological inexactitude.” But lying? No, never. As Mr. Speaker always reminds us: these are honorable people.

So when Boris Johnson, former prime minister, went before the House of Commons Committee of Privileges on Wednesday accused of lying to Parliament on four separate occasions, it was serious. The committee isn’t a court: it applies parliamentary law, not the laws of the land, and its members are politicians, not judges. But it has the power to possibly end Johnson’s political career if it finds against him.

The committee is trying to adjudge whether Johnson lied to Parliament about attending parties in Downing Street when the country was under strict coronavirus restrictions. To recap: Johnson had told Parliament that no parties had taken place and that all coronavirus regulations had been followed completely. But a sea of evidence contradicting him quickly leaked out. Hence what is familiarly known as “Partygate.”

You could tell how serious the situation was because the habitually scruffy Johnson appeared to have brushed his hair and done up his tie. He also had a top lawyer sitting behind him. Advice from Lord Pannick, King’s Counsel—what the British call a “silk”—is not cheap.

The problem is that Johnson, as even his fans will admit, has only a nodding relationship with the truth. It’s as if the truth were an acquaintance he sees across a crowded room but hopes not to meet, as he’s completely forgotten its name.

With that clearly in mind, Harriet Harman, the chairwoman of the committee, began proceedings with a statement saying that Britain’s entire democracy depended on M.P.’s not fibbing. “I swear to tell the whole truth,” said Johnson, clutching a Bible, hoping it wouldn’t catch fire.

Even so, the committee was careful about using the L word. The issue was whether he’d “misled the House.” Johnson conceded he may have done this “inadvertently.” The committee has to decide if he had lied deliberately or recklessly. Should they find him to have done so—effectively ruling that he was in contempt of Parliament—they can recommend penalties, such as banning him from Parliament. This ban may be short, but if it lasts for 10 or more days, it would trigger a recall petition, almost certainly leading to a by-election in his West London seat of Uxbridge and South Ruislip. If he lost this by-election—and it is not a safe seat—he would be thrust out of politics.

Boris as Pinocchio: on the plus side, it does at least suggest he has a conscience.

Johnson felt this was terribly unfair. He had personally followed all the rules, he insisted, and it was only after he left the room that rules may have been broken by others. No one had thought to tell him if they had. Anyone who says different, such as former chief adviser Dominic Cummings, can’t be trusted like Honest Boris.

Not even the architecture could be relied upon. Downing Street, Johnson said, was both “a cramped, narrow 18th-century town house” in which keeping a required distance is near impossible and yet so vast he couldn’t hear drunken antics in the room beside his office. “I knew nothing” was his predominant defense. Ms. Harman called it “flimsy,” and she wasn’t talking about the walls.

Johnson had repeatedly told Parliament that “all [coronavirus] guidance had been followed,” which, as photos given to the committee showing him in undisguised (and unmasked) revelry revealed, was clearly not true. He explained this by saying that he had “misremembered” what he had previously told M.P.’s. When he said guidance was followed “completely,” he meant “to the best of my ability.” In any case, these were essential “work events,” definitely not parties.

“I swear to tell the whole truth,” said Johnson, clutching a Bible, hoping it wouldn’t catch fire.

Yes, there was a birthday celebration, but only a tiny one. Yes, his wife’s interior designer had attended, seemingly contradicting the idea that it was a work event, but she’d barely “popped her head” in. The important thing was that the cake had remained in its box, and no one had sung “Happy Birthday.” Similarly, a farewell gathering at which he was seen raising a glass to a roomful of colleagues was simply about lifting morale. “I’ll believe to the day I die that it was part of my job to thank people for the work they had done,” he said. Some thought this comment lacked tact considering Mr. Johnson’s coronavirus regulations had prevented many people from being with their loved ones in hospitals on the day they had died.

Mr. Johnson’s word of the day, deployed often over three hours, was “inconceivable.” There was simply no way he would be so reckless, Mr. Johnson self-assessed, and so logically he hadn’t been. If anyone seriously thought those activities were not permitted, would he have been so stupid as to have allowed a photographer?

“Hand on heart, I did not lie,” he said. “Those statements [made to Parliament] were made in good faith.” And yet, before making them, he had relied only on the advice of his political yes-men. Jack said it was fine, so I assumed it was. “Why didn’t you take proper [legal] advice?” asked Sir Bernard Jenkin, a Tory veteran. Boris could only burble.

By coincidence, this all happened 60 years to the day after the telling of the most notorious lie in Parliament’s history. On March 22, 1963, John Profumo, the secretary of state for war, denied in the House of Commons that he had shared a girlfriend with a Russian diplomat. He would resign within three months.

The prime minister at the time, Harold Macmillan, was known for unflappability, illustrated by a line from Gilbert and Sullivan’s Gondoliers pinned to his office door. “Quiet, calm deliberation disentangles every knot,” it said. It seems that Mr. Johnson is also motivated by a line from those same songwriters but from H.M.S. Pinafore: “What, never? Well, hardly ever!” We wait to see if “hardly ever” can save his career. The committee is expected to publish its report after Easter.

Patrick Kidd is the editor of the Diary column in The Times of London. A collection of work from his time as parliamentary sketch writer, The Weak Are a Long Time in Politics, was published in 2019