The Tory beat Labour incumbent Ken Livingstone in last week's vote, and will give up his Henley and Thame constituency following a by-election after the summer recess.

It is understood that among those interested in taking on the role is Mr Johnson's father Stanley, 67.

Chairman of the Thame branch of South Oxfordshire Conservatives, Michael Welply, said he was confident that until his replacement Mr Johnson would still be able to perform his duty to his constituency, while at the same time running the capital.

"When people ask how can he do two jobs, the same might be said of cabinet members and the Prime Minister. I expect Boris to continue to fulfil his commitments as a Member of Parliament for his area.

"If people have a concern they can still contact him and he will deal with it and he will more than likely come down and run his surgeries. The guy is a workaholic- he's on the job for about 20 hours a day."

He paid tribute to Mr Johnson, adding that he would be sad to see him go.

"We are delighted he had such an outstanding victory because London really deserves better. He's been a brilliant constituency MP and was very even-handed, holding his surgeries all around the constituency. He has a house in Thame and one often saw him wandering through Waitrose dressed in a T-shirt and with a pair of old trainers on his feet.

"Beneath his humourous exterior there is a very serious mind. But none of us want to go through life being Mr Grim - we have that with the current Prime Minister for goodness sake."

Refusing to be drawn on the possibility of Mr Johnson Snr becoming Thame's new MP, he said that the candidate for the by-election would be chosen in an orderly and thorough manner.

With a current 12,000 seat majority over nearest rivals The Lib Dems, Mr Welply is confident that a Tory would prevail.

He said: "There's a very, very strong Conservative presence here. We are looking for someone who we believe will represent South Oxfordshire in the long term."