Former Tory leadership candidate Rory Stewart has said he will be standing down at the next general election and has resigned from the Conservative Party. 

The Penrith and The Border MP ran against Mr Johnson in the race to lead his party in June, but on Friday he announced his decision to quit.

READ MORE: Rebecca McQuillan: Jackson Carlaw is sending Scots Tories into reverse

Mr Stewart tweeted: “It’s been a great privilege to serve Penrith and The Border for the last ten years, so it is with sadness that I am announcing that I will be standing down at the next election, and that I have also resigned from the Conservative Party.”

He has since announced he is going to stand as an independent candidate to be Mayor of London, he has announced.

The 2020 mayoral election will pit him against Labour incumbent Sadiq Khan and Conservative candidate Shaun Bailey, who was backed by Mr Johnson in his Tory conference speech on Wednesday.

Mr Stewart warned of the danger of Brexit to the capital and said he wanted to combat “extremism” in British politics as London mayor.

“I’m leaving that Gothic shouting chamber of Westminster, I’m getting away from a politics which makes me sometimes feel as though (US President Donald) Trump has never left London,” he said.

Mr Stewart served as international development secretary until his resignation from Government in July, shortly before Mr Johnson took office and undertook his drastic Cabinet reshuffle.

READ MORE: Court to be asked if PM can be jailed over No Deal 

The firm opponent of a no-deal Brexit was among the rebels who voted to take control of the Commons timetable in order to pass legislation aimed at blocking a sudden exit from the EU.

The PM retaliated by ordering the controversial cull, which saw two former chancellors stripped of the Conservative whip.

Reacting to the news, Amber Rudd tweeted: "What a loss to politics, an outstanding MP and Minister. One of the strongest speakers in Parliament. Principled, patient, thoughtful. I feel certain he’ll be back."