Jeremy Hunt has accused Boris Johnson of cowardice after the favourite to become the UK’s next prime minister refused to discuss the noisy altercation with his girlfriend.

Writing in The Times, the foreign secretary said his rival was “pathetically” avoiding questioning and trying to ”slink through the back door” of No 10.

“Don’t be a coward Boris,” Mr Hunt wrote as he urged the Tory frontrunner to show up to a Sky News debate on Tuesday. “Man up and show the nation you can cope with the intense scrutiny the most difficult job in the country will involve.”

Meanwhile, on a visit to Scotland, Mr Hunt denied he was trying to make character a central issue in the contest, because everyone had something they “would be embarrassed” about, if it emerged.

But, asked if Mr Johnson was right to refuse, repeatedly, to explain the screaming row at the flat he shares with his girlfriend, the underdog in the Tory leadership race replied: “I think someone who wants to be prime minister should answer questions on everything.”

Biggest lies told by Boris Johnson Show all 5 1 /5 Biggest lies told by Boris Johnson Biggest lies told by Boris Johnson Made-up quote for The Times Johnson was sacked from The Times newspaper in the late 1980s after he fabricated a quote from his godfather, the historian Colin Lucas, for a front-page article about the discovery of Edward II’s Rose Palace. “The trouble was that somewhere in my copy I managed to attribute to Colin the view that Edward II and Piers Gaveston would have been cavorting together in the Rose Palace,” he claimed. Alas, Gaveston was executed 13 years before the palace was built. “It was very nasty,” Mr Johnson added, before attempting to downplay it as nothing more than a schoolboy blunder. PA Biggest lies told by Boris Johnson Sacked from cabinet over cheating lie Michael Howard gave Boris Johnson two new jobs after becoming leader of the Conservatives in 2003 – party vice-chairman and shadow arts minister. He was sacked from both positions in November 2004 after assuring Mr Howard that tabloid reports of his affair with Spectator columnist Petronella Wyatt were false and an “inverted pyramid of piffle”. When the story was found to be true, he refused to resign. PA Biggest lies told by Boris Johnson Broken promise to boss In 1999 Johnson was offered editorship of The Spectator by owner Conrad Black on the condition that he would not stand as an MP while in the post. In 2001 he stood - and was elected - MP for Henley, though Black did allow him to continue as editor despite calling "ineffably duplicitous" PA Biggest lies told by Boris Johnson Misrepresenting the people of Liverpool As editor of The Spectator, he was forced to apologise for an article in the magazine which blamed drunken Liverpool fans for the 1989 Hillsborough disaster and suggested that the people of the city were wallowing in their victim status. “Anyone, journalist or politician, should say sorry to the people of Liverpool – as I do – for misrepresenting what happened at Hillsborough,” he said. PA Biggest lies told by Boris Johnson ‘I didn’t say anything about Turkey’ Johnson claimed in January, that he did not mention Turkey during the EU referendum campaign. In fact, he co-signed a letter stating that “the only way to avoid having common borders with Turkey is to vote Leave and take back control”. The Vote Leave campaign also produced a poster reading: “Turkey (population 76 million) is joining the EU”

Mr Hunt added: “I am not going to comment on Boris’s personal life. That’s for others to make their judgments on.”

“What Boris needs to do is engage properly in this leadership debate, not to shy away from the Sky News live debate which is scheduled for Tuesday evening which he’s been invited to.

“I’ve said I’m willing to go to. This is an audition to be the prime minister of the United Kingdom.”

Mr Hunt’s comments, on a visit to Scotland, came after one of his key allies, trade secretary Liam Fox, said of Mr Johnson’s stonewalling: “It’s always easier to just give an explanation.”

The fresh focus on the dispute comes after the favourite in the race for No 10 suffered a major slump in popularity in the wake of the incident, as voters said his private life does matter.

Mr Johnson’s lead among Conservative voters has more than halved since the incident in the early hours of Friday morning – and rival Jeremy Hunt has snatched the lead among the wider public.

More than half of voters said Mr Johnson’s private life was relevant to his ability to be prime minister and three-quarters said a candidate’s character was relevant to the contest.

“It is unusual to see a politician’s private life having this level of salience among voters,” said Damian Lyons Lowe, chief executive of pollsters Survation.

Mr Johnson has refused to give an explanation for the banging and screaming heard at the flat he shares with Carrie Symonds, despite it casting a shadow over his bid for No 10.

Asked about the incident at the first leadership hustings in Birmingham, Mr Johnson said people didn’t “want to hear about that kind of thing”.

He added that the audience of party members were more interested in what his “plans are for my country and for the party”.

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In a recording obtained by The Guardian, Carrie Symonds, Mr Johnson’s girlfriend, was reportedly heard screaming and telling him to “get off me” and “get out of my flat”.

The tape is also said to reveal Mr Johnson shouted at Ms Symonds to “get off my f***ing laptop” before a loud crashing noise was heard.