LONDON — It is a tradition, and not a very pretty one, for candidates for high office in Britain to submit themselves to a grueling, often excruciating, one-on-one interview with BBC presenter Andrew Neil.

It is a very British thing. Neil and his anxious quarry sit in facing chairs, the erudite, orotund-voiced, imposing BBC inquisitor holding in his fists sheafs of paper with lots and lots of uncomfortable facts.

The 30-minute probes can be forensic, almost medical. They can also be a bit of a bear pit. But generally the interviews make for great telly, especially in the last days of an election.

Now, bucking all precedent, Prime Minister Boris Johnson has canceled his appointment in the dentist chair with Neil.

This has suddenly become a surprising, serious issue in the campaign.

On Thursday night, Neil issued a remarkable, unprecedented on-air challenge to Johnson, and he did so on the state-supported BBC, where he suggested that Johnson might be a coward or a fabricator.

“It is not too late,” Neil said in a monologue to the audience. “We have an interview prepared. ­Oven-ready, as Mr. Johnson likes to say.”

Eyeballing the camera, Neil pounced: “The theme running through our questions is trust — and why at so many times in his career, in politics and journalism, critics, and sometimes even those close to him, have deemed him to be untrustworthy.”

Neil then ticked off a list of questions Johnson has miffed, from his dubious claims of how many hospitals his Conservative Party will build, to the impact of his Brexit deal on Northern Ireland, to fleshing out his fuzzy math on the hiring of 20,000 new police officers.

Johnson, a former president of the Oxford Union debate society and no duffer himself in polysyllabic combat, fired back Friday, disparaging Neil as a real “Lord Buckethead,” a British satirical candidate fronting a frivolous political party.

Johnson says he’s done plenty of press — what’s one more interview?

And Johnson and Labour Party leader Jeremy Corbyn did participate in a second and final face-to-face debate on the BBC on Friday night. This format allowed for the open-ended answers, stump-speeching and desultory follow-up typical of the forums.

The two leaders broke little new ground. In one exchange, Corbyn said, “Socialism carried out in a democratic way in this country and Scandinavia and other places has raised living standards of the very poorest . . . and our Labour government will do the same again.”

He said that his socialism “doesn’t leave people behind.”

Johnson countered that his kind of “conservatism understands the importance of a dynamic market economy that is the only way you can pay for fantastic public services and for looking after the poorest and neediest in our society.”

He said, “To attack capitalism . . . is absolutely senseless.”

In the row over appearing with Neil, Michael Gove, a senior Conservative, defended Johnson on Friday, saying the prime minister has given more than 100 interviews during the five-week election campaign, allowing an “unprecedented level of scrutiny.”

And if you’re 10 points ahead in the polls, as Johnson and the Conservatives are, why offer yourself as a happy meal to a Rottweiler on prime-time TV?

One reason: A YouGov poll published Friday found that 67 percent of the British public said Johnson should do the interview; 13 percent said he shouldn’t.

Many wonder what Johnson has to fear.

Neil is a former editor of Rupert Murdoch’s Sunday Times and chairman of the holding company that owns the weekly Spectator magazine, a bible for the Tory smart set, where Johnson was once editor.

He has a reputation as a bit of a grumpy old man, but one who’s ready to tear into all candidates with more or less equal appetite.

An unnamed campaign official from the Conservative Party told British reporters on Friday: “The public are fed up with interviews that are all about the interviewer and endless interruptions. The format is tired and broken and needs to change if it is to start engaging and informing the public again.”

To which Neil replied that his “tired” Corbyn interview got 3.2 million viewers and that the Tories posted it on Facebook. “So not that tired,” the BBC’s man tweeted.

He added that the Conservative “source” represented a “pyramid of piffle.”

Tory fighting words.

Ian Lavery, Labour Party chair, accused Johnson of thinking that “he’s born to rule and doesn’t have to face scrutiny.” He added that Johnson was “running scared.”

All the major candidates have appeared on Neil’s show. He’s grilled Nigel Farage of the Brexit Party, Jo Swinson of the Liberal Democrats and Nicola Sturgeon of the Scottish National Party.

It is only Johnson who has dodged his ball.

This peeves Labour. If Corbyn was shredded, the argument goes, Johnson deserves the same.

Labour officials have accused the BBC of bias in its coverage of the general election. They say they agreed to Corbyn’s interview with Neil with the “clear understanding” that Johnson would also face a half-hour in the hot seat.

The prime minister has been notably absent from several debates. He was memorably replaced by a melting ice sculpture last week during a party leaders debate on climate change. On Thursday, broadcaster ITV announced that Johnson was refusing to do an interview with Julie Etchingham, another heavy-hitting journalist.

In his on-air challenge to Johnson, Neil said that if the prime minister were sitting before him, he’d ask about Johnson’s pledges on health care and security. He’d also ask about Johnson’s Brexit deal and whether it effectively puts a border down the Irish Sea.

“He vows that the NHS [the National Health Service] will not be on the table in any trade talks with America. But he vowed to the DUP, his Unionist allies in Northern Ireland, that there would never be a border down the Irish Sea,” Neil said. “That is as important to the DUP as the NHS is to the rest of us. It is a vow his Brexit deal would seem to break.”

Neil said, “There’s no law, no Supreme Court ruling that can force Mr. Johnson to participate in a BBC leaders’ interview.”

But, he added, “the prime minister of our nation will, at times, have to stand up to President Trump, President Putin, President Xi of China. So it was surely not expecting too much that he spend half an hour standing up to me.”