The comments are the first suggestion from anyone close to the London mayor he would consider running for the leadership from outside the House of Commons.

Adding his voice to the growing number speculating over the future of the leadership of the Conservative party Stanley Johnson said: “It would not be a reasonable expression of the way things are if there were to be an election in the Tory party for leader under whatever rules they have – it just wouldn’t be reasonable if Boris somehow was not able to be a candidate.”

To allow a contender from outside Westminster the Conservative party rules would need to be rewritten. However the change it would allow Mr Johnson, who is seen by many as a natural successor to David Cameron, to focus on being Mayor of London without running an election or by-election campaign.

Stanley Johnson used the Conservative leadership campaign of 1963 as a comparison. Alec Douglas-Home won from the House of Lords, and then quickly renounced his peerage and won a safe Conservative seat. “Alec Douglas-Home was not a member of the House of Commons, he was a peer. But they found a way.

“Don’t tell me it wouldn’t be possible to have a system whereby you say: OK, life has moved on, there are now important elective offices.”

He added: “How reasonable would it be to exclude the mayor of a major city?”

The comments follow earlier reports that Mr Johnson was left furious following claims that the Chancellor had made a “personal approach” urging him to stand as an MP.

A source close to Mr Johnson distanced the Mayor of London from the reports, insisting that there is “no civil war” between the two men and that Mr Johnson has yet to decide if he will stand in 2015.

Speaking to LBC Radio earlier this month, Mr Johnson ruled out any attempt to re-enter the Commons before 2015, and indicated he wanted to serve out his full term as mayor, which runs to 2016.

“I am so sick of this subject, I think I’m going to expire sometimes. I am going to get on with my job as mayor of London,” he said.

“The answer is I am sticking to my job that I was elected to do in 2012 and indeed in 2008. I’m very, very privileged to be here.”