Boris Johnson, the strong favourite to become Britain's next prime minister, came under pressure from figures in his own party on Sunday to explain reports of a domestic 'row' that led to a police visit.

Although still heavily backed to beat Jeremy Hunt to become Conservative Party leader, and therefore prime minister, a snap poll published in the Mail on Sunday suggested that the incident had cut his support.

The Guardian reported that police were alerted early on Friday after a neighbour heard a loud altercation involving screams, shouts and bangs at the south London property, shortly after Johnson had secured his place in the final run-off to become prime minister.

The paper said Johnson's partner Carrie Symonds could be heard telling the former London mayor to "get off me" and "get out of my flat".

The former foreign secretary refused to answer questions about the incident on the first day of the month-long contest to win over Conservative grassroot members, saying "I don't think people want to hear about that kind of thing."

He instead tried to focus on his policies, saying "we need to get Brexit done" and promising to prepare Britain for a no deal exit from the EU, if a deal cannot be reached.

Leaflets in support of Conservative MP Boris Johnson are seen displayed at a Conservative Party leadership hustings event in Birmingham, central England on June 22, 2019. - Britain's leadership contest starts a month-long nationwide tour on Saturday as Boris Johnson and Jeremy Hunt reach out to grassroots Conservatives in their bid to become prime minister. (Photo by Oli SCARFF / AFP)

- 'Lack of discipline' -

Tory grandee Malcolm Rifkind criticised the response, saying "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," he told BBC Radio 5.

Former Tory foreign office minister Alan Duncan told the Guardian his former boss now had a "big question mark over his head", adding Johnson had shown a "lack of discipline" throughout his career.

Among all voters, Hunt is now the preferred candidate to become prime minister, according to the Survation poll in the Mail on Sunday, as Johnson saw a seven percent decline in support.

He also saw his lead over Hunt with Tory voters slashed from 27 percent to nine percent since Friday.

But it is the party's 160,000 members who will have the final say, and their support appeared undimmed during the first day of "hustings" -- internal party debates to decide the new leader -- in Birmingham, central England, on Saturday.

The crowd gave Johnson a standing ovation, and loudly heckled interviewer Iain Dale as he quizzed the former London mayor over Friday's domestic incident.

- Bannon claims -

"Stuff happens at home all the time... someone spills the wine, we can't really be making headlines out of that," supporter Hasnain Ahmed, 23, told AFP.

"What's important is what's this guy going to be delivering for you in Brexit."

With Sunday marking the three-year anniversary of the vote to leave the EU, the issue still dominates British politics.

Hunt also received a warm reception, promising that if he couldn't strike a Brexit deal with the EU, "then I will leave without a deal".

"I was probably leaning towards Boris but I was very impressed with what Jeremy Hunt said today," Tory councillor Karen Shakespeare, told AFP.

"He surprised me with his directness and honesty so I have to say I am now leaning very heavily towards Jeremy Hunt."

Johnson also came under scrutiny on Sunday for his relationship with Steve Bannon, the controversial former adviser to US President Donald Trump.

Footage published by the Observer showed Bannon claiming that he had helped craft Johnson's resignation speech as foreign minister last year.

The pair got to know each other professionally when both were in office, and were reported to have met again in an unofficial capacity last summer.

Johnson said at the time that "the so-called relationship" with Bannon was a "lefty delusion" and his office dismissed the latest claims of a working relationship as "totally preposterous to the point of a conspiracy". (AFP)

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