London (CNN) Boris Johnson , the front-runner in the race to become Britain's next prime minister, was facing mounting calls Sunday to fully explain an incident in which police attended an alleged altercation at the London home he shares with his girlfriend.

Jeremy Hunt, Johnson's rival for leadership of the Conservative Party, said in a piece for The Times of London on Monday that he was not interested in Johnson's private life, but challenged his opponent to provide an explanation to the public about both his policies and the incident.

"Scrutiny of the candidates matters. One of the strengths of our system is that we scrutinise our politicians with more intelligent ferocity than anywhere in the world," Hunt wrote

"Don't be a coward Boris, man up and show the nation you can cope with the intense scrutiny the most difficult job in the country will involve."

International Trade Secretary Liam Fox told the BBC that while Johnson's private life "does not concern me," he added: "I think it is always easier to just give an explanation."

Former Conservative Foreign Secretary Malcolm Rifkind also told the BBC: "If you are a candidate to be prime minister and the police have been called to your house -- fairly or unfairly -- the fact is there was a police visit. You don't just say 'no comment.'

"That implies you may have something you don't want to disclose."

Rifkind, who has hinted he might back Hunt in the race to be the next Conservative leader and by extension the next PM, added: "It was a lack of judgment to refuse to even make a short comment. All he could have said, quite reasonably, would have been that in all relationships there are occasionally outbursts of anger and disagreement."

Labour opposition politician Andrew Gwynne said Sunday Johnson was "completely unsuitable" to be PM.

He told Sky News: "In one sense, of course, it is a private matter, but when you're running for public office, when you are wanting to be the prime minister of the UK, then these matters are in the public interest."

But Gwynne added that Johnson's actions as a politician were more important. "I just think his record throughout his time both as mayor of London -- wasting money on the garden bridge, wasting money on Routemaster buses, wasting money on water cannon that couldn't be used -- through to his disastrous tenure as foreign secretary just renders him completely, I think, unsuitable to be the prime minister of our great country."

Was there ever a man less suited to be Prime Minister?https://t.co/GnxWGMwrKm — Keir Starmer (@Keir_Starmer) June 21, 2019

Labour Brexit spokesman Keir Starmer tweeted the Guardian's initial story about the alleged dispute with the comment, "Was there ever a man less suited to be Prime Minister?"

Boris Johnson attends the first leadership hustings on Saturday in Birmingham.

Johnson evades questions

In the town hall event in Birmingham, Johnson was asked at least four variations of the question by Dale, who finally suggested Johnson was simply not going to answer the question.

"I think that's pretty obvious," the former foreign secretary and leading Brexiteer said.

The Guardian reported late Friday that a neighbor of Johnson's girlfriend Carrie Symonds had heard an argument from her apartment, knocked on the door, got no response, and called the police.

The neighbor, who reportedly recorded the altercation, told the Guardian that Symonds could be heard telling Johnson "get off me" and "get out of my flat."

In the recording, Symonds said Johnson had ruined her sofa with red wine. "You just don't care for anything because you're spoilt. You have no care for money or anything," she said according to the Guardian.

Johnson was also heard saying "get off my f***ing laptop" before a loud crashing noise, the paper reported.

The Metropolitan Police issued a statement confirming that a "caller was concerned for the welfare of a female neighbour."

The police arrived and "spoke to all occupants of the address, who were all safe and well," adding: "There were no offences or concerns apparent to the officers and there was no cause for police action."

But they did not name Johnson or Symonds as being involved in the incident.

Symonds has not made a public comment about the incident, which is reported to have happened in the early hours on Friday.

Boris Johnson resigned as Foreign Secretary in 2018 over Theresa May's Brexit plan.

'Fictitious allegations'

Johnson's neighbor Tom Penn declined to comment to CNN on the story, referring to a statement he issued to the Guardian in which he defended his decision to record the alleged argument.

Penn said he was downstairs collecting food from a takeaway delivery driver when he heard "shouting."

"I went inside my own home, closed the door, and pressed record on the voice memos app on my phone," he told The Guardian, explaining his decision to record the noise.

"To be clear, the recordings were of the noise within my own home. My sole concern up until this point was the welfare and safety of our neighbours. I hope that anybody would have done the same thing," he added.

Penn said he contacted the newspaper because he felt "it was of important public interest".

"I believe it is reasonable for someone who is likely to become our next prime minister to be held accountable for all of their words, actions and behaviours," he explained

Penn said he voted Remain in the EU referendum but since contacting the Guardian he and his partner have been the target of "fictitious allegations" by "some areas of the press."

Many of Britain's Conservative party-backing tabloid newspapers on Sunday suggested that Penn and his girlfriend reported the incident to police because of their political leanings. The Sun newspaper called the couple "left-wing playwrights" and the Daily Mail reported they had seen anti-Conservative tweets on her Twitter account, which has now been deleted.

'A non story'

The story has shaken up the race to be next Conservative leader, and has led most British newspapers. Some of Johnson's backers tried to play the story down. Iain Duncan Smith, a former Conservative Party leader, told CNN: "This is a private matter."

And Security Minister Ben Wallace, who nominated Johnson to be Conservative Party leader, was dismissive of the Guardian newspaper report in a tweet.

"What a non story 'couple have row.' Lefty neighbours give recording to Guardian. Newspaper reaches new low is a better news story," Wallace tweeted at Sun journalist Tom Newton-Dunn. Wallace deleted the tweet eight minutes after posting it, but it was archived by the Twitter feed Tweets MPs Delete.

Johnson took part in the leadership hustings with his rival for the party leadership, Jeremy Hunt. The 160,000 Conservatives are preparing to vote for their favored candidate, with the winner due to be announced next month.

Hunt replaced Johnson as Foreign Secretary after Johnson resigned in protest at UK Prime Minister Theresa May's Brexit plan.

Until this weekend's story broke, Johnson was the favorite to win the leadership race, pitching himself as the only man to take the UK out of the European Union on October 31. Hunt has said he would also support a no deal exit if necessary.