London Mayor Boris Johnson has admitted he can drink "an awful lot" at lunch before carrying on with the rest of his working day.

Mr Johnson made the comment during an interview about his new book on his hero wartime Prime Minister Sir Winston Churchill.

Referring to Churchill's remarkable work-rate despite a regular intake of alcohol throughout the day, Mr Johnson said: "I mean, what was he on? How did he do it?

"He was incredible ... I mean, I can drink an awful lot at lunch and then write very fluently and fast, but if I drink at dinner, it just peters off," he said in the interview with the Radio Times.

Boris Johnson has written a book on his political hero Sir Winston Churchill. Credit: PA Wire

During the interview, Mr Johnson said he had "changed as a politician" since becoming Mayor in 2008.

He said: "The experience of running London for six or seven years has shown me what you have to do to get things done, and the energy and the application you have to put into it."

His decision to stand as Conservative candidate for Uxbridge and South Ruislip in the General Election has been widely tipped as preparation for an eventual party leadership bid.

But asked whether his new book mounted to a covert leadership manifesto, he said: "No. No, I absolutely swear it isn't."

Mr Johnson also denied seeking to compare himself to his political hero in the book, called The Churchill Factor.

He said he was "genuinely obsessed" by Churchill, who he believes would have been in favour of renegotiating Britain's EU membership before an in/out referendum.