The favourite for the UK tory leadership declined to explain to party supporters what went on at the south London flat in the early hours of Friday morning, saying "they did not want to hear about that kind of thing".

Mr Johnson's campaign for Number 10 was rocked by the revelations that officers were called to the home he shares with partner Carrie Symonds by a neighbour who claimed to have been "frightened and concerned" after hearing shouting, "a loud scream" and banging coming from the property.

A poll carried out after the reports emerged suggested Mr Johnson's support among Tory voters had dropped by more than half, while among the general electorate it indicated he had slipped into second place behind rival Jeremy Hunt.

Tory elder Sir Malcolm Rifkind told BBC Radio 5 Live: "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."

Sir Malcolm, who indicated he would back Mr Hunt in the race, 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."

Two surveys suggested Mr Johnson's lead over Mr Hunt among Conservative voters had been cut from 27 points to 11, while among all respondents Mr Hunt was ahead on 32% with Mr Johnson on 29%.

Mr Johnson insisted at the hustings he was the one to "get Brexit done" and put his record at City Hall at the heart of his pitch.

Meanwhile Mr Hunt, who will visit Scotland on Sunday, revealed a pledge to exempt hundreds of thousands of firms from business rates if he becomes prime minister.

The rivals are battling to win the support of 160,000 Tory party members who will choose their next leader, and the prime minister, in July.

Australian Associated Press