Britain's leadership contest was rocked on Saturday by reports that police were called to a late-night "row" between frontrunner Boris Johnson and his partner, just hours before campaigning opened to win over grassroots Conservatives.

The Guardian said officers were alerted early on Friday after a neighbour said there had been 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 late Friday Johnson's partner Carrie Symonds could be heard telling the former London mayor to "get off me" and "get out of my flat."

London's Metropolitan Police said it responded to a call from a local resident but that "all occupants of the address... were all safe and well".

Johnson, who is the runaway favourite to beat Jeremy Hunt, refused to answer questions on the issue during the first date of a month-long nationwide tour he is conducting with Hunt to win over Conservative members, who have the final say.

"I don't think people want to hear about that kind of thing," he told interviewer Iain Dale, to cheers from a friendly crowd at the first of 16 "hustings" - where candidates field audience questions.

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.

Whoever takes the Tory party leadership in the week beginning July 22 - and therefore becomes prime minister - will face the looming Brexit deadline of October 31. 

But the race might ultimately turn into a popularity contest between Johnson - pugnacious but affable with a tendency for gaffes - and the more diplomatic, low-key Hunt.

The "row" was splashed across the front pages of most newspapers on Saturday, and while bookmakers were still betting for Johnson, pundits warned the incident could harm his chances.