Sibling rivalry behind Britain's Brexit politics

Rachel Johnson -- sister of arch Conservative Brexiterr Boris Johnson -- at the launch of the new pro-EU political party, Change UK (AFP Photo/Adrian DENNIS)

London (AFP) - Rachel Johnson, the sister of leading Brexit proponent Boris Johnson, on Tuesday became a candidate for new pro-EU party Change UK -- the latest high-profile sibling split over the contentious issue.

The former Financial Times and Daily Telegraph journalist, 53, joined the new party formed by 11 cross-party europhile MPs, to run in the upcoming European Parliament elections.

She is the younger sister of former foreign secretary Boris, who is favourite to take over as prime minister after current leader Theresa May steps down once the first phase of Brexit is completed.

"I'm sure that Boris understands why this is not a vote against Boris," she said, telling London's Evening Standard newspaper she felt "impelled to stand up and be counted for what I believe in".

The ardent European Union supporter once said she would "walk down Whitehall in my birthday suit to stop Brexit."

She now writes a weekly column in The Mail on Sunday, and was unveiled on a roster of candidates for Change UK at an event in Bristol in southwest England.

Boris Johnson was a key figure helping swing the 2016 referendum vote in favour of Leave.

He has criticised May's withdrawal deal struck with the EU for keeping Britain too closely tied to the bloc, putting him at odds with other members of his family.

His brother Jo, also a Conservative politician, quit as a minister in November, believing May's deal would sever too many ties with the EU.

He has since backed calls for a second referendum on the issue.

The power of Brexit to cut across family bonds -- even if on the same side -- was also evident earlier this month.

Annunziata Rees-Mogg, brother of influential Conservative Brexiteer Jacob Rees-Mogg, announced she was leaving the party to stand as a candidate for Nigel Farage's new Brexit Party.

Her brother tweeted that "Annunziata would be a brilliant prime minister but I hope as a Tory".

It was revealed she has been a member of the Conservatives since the age of five.