Former Conservative leadership candidate Rory Stewart is going to stand as an independent candidate to be Mayor of London.
The former International Development Secretary quit the Tory Party on Friday morning and announced his intention to stand down at the next general election.
The Penrith and The Border MP was among the 21 rebels who had the whip removed by Boris Johnson when he defied him in the Commons by backing a move designed to block a no-deal Brexit.
In June he ran against Mr Johnson in the race to lead his party.
Mr Stewart says he plans to walk through every borough of London before London's mayoral election in 2020.
He will run against the current Mayor of London Sadiq Khan, Shaun Bailey the Conservative candidate, the Liberal Democrats Siobhan Benita and Green Party leader Sian Berry.
In an announcement this morning Mr Stewart said London is "a city in real danger".
"Danger from Brexit, from technological change but I think, above all, from what's happened in British Politics. The kind of extremism that is taking over country."