The willingness to put career ahead of family is a character trait unique to left-wing people, Boris Johnson has said.
In an interview with The Australian newspaper, the mayor of London dismissed the suggestion that he had a rivalry with his brother Jo that echoed that between Ed and David Miliband.
"We don't do things that way, that's a very left-wing thing," he said when asked about the Labour brothers' battle for the leadership of their party.
"Only a socialist could do that to his brother, only a socialist could regard familial ties as being so trivial as to shaft his own brother. I mean, unbelievable! Only lefties can think like that," he said.
"They see people as discrete agents devoid of ties to society or to each other, and that's how Stalin could murder 20 million people."
Jo Johnson, the MP for Orpington and Boris' younger brother, was recently appointed by David Cameron to head up his Downing Street policy unit.
Asked whether he thought Jo would make a good prime minister, Boris replied: "I think it very likely and I think he'd be brilliant."
It is widely believed that Boris has his eyes on a return to the Commons and No.10 himself once his second term as mayor ends in 2016.
However it was recently reported that he has decided against standing for election to parliament at the 2015 general election in order to be in a position to challenge for the Tory leadership should David Cameron fail to secure victory.
In the interview Boris also praised the contribution of immigrants to the capital. "I think 40 per cent of Londoners were born abroad; immigration's been the lifeblood of London," he said.
The mayor recently repeated his suggestion that illegal immigrants who had been in the country for more than 12 years be given amnesty - a policy rejected by David Cameron.
"You've got people who are living here, ultimately you've got to reflect a reality," he said in July. "Otherwise they are not engaged in the economy, they are not being honest with the system, they are not paying their taxes, it is completely crazy."
Boris' visit to Australia comes in the middle of that country's general election campaign.Suggest a correction