London's flamboyant mayor Boris Johnson plans to renounce his US citizenship to prove his "commitment to Britain", the Sunday Times reported, although he denied suggestions he wanted to become prime minister during last week's visit to the US.

The mop-haired Johnson, who was born in New York in 1964, holds British and US passports.

He recently settled a capital gains tax bill sent by the US after he sold his house in north London, calling the demand "absolutely outrageous."

All US citizens have to pay tax to Washington, even if they live outside the country.

But Johnson told the newspaper that his intention to renounce his US passport was due to patriotic reasons, although admitted the process may not be straightforward.

He said his US passport was "an accident of birth" and that he had to "find a way of sorting it out" with US ambassador Matthew Barzun.

"The reason I'm thinking I probably will want to make a change is that my commitment is, and always has been, to Britain," he added.

"They (the Americans) don't make it easy for you."

Johnson hopes to make a return to British national politics in May's general election, standing for a seat in the London suburbs, opening the way for a push for the top job.

Although not an insurmountable obstacle, constitutional experts warn that dual citizenship could throw up difficulties in any bid to become prime minister.

During his recent six-day visit to Boston, New York and Washington -- officially billed as a trip to strengthen US ties with London, but seen as many as a chance to raise his international profile -- Johnson insisted he had "no ambition" to replace David Cameron as Conservative leader and prime minister.

"It may be that some babe unborn will take over from Prime Minister Cameron, but it isn't going to be me," he told reporters in Washington. AFP, photo by AFP