Penrith and the Border MP Rory Stewart is planning to stand to become the Mayor of London.

The shock annoucement - made on Twitter in the last few minutes - came after the Cumbrian MP and former international devleopment secretary said he would stand down as an MP after nine and a half years in the job.

A previous London Mayor was Boris Johnson.

Writing about his decision, which has come after months of his public opposition to Prime Minister Boris Johnson and the possibility of a damaging no-deal Brexit under his premiership, the MP said he feared the UK's mainly two party system was falling apart.

The MP was among 21 Conservative Party members who were thrown out of the Conservative Party for voting against the government to pass a law that they hope will block a no-deal brexit by making it illegal.

In a video the he posted online, Mr Stewart was scathing about the state of current UK politics, describing the House of Commons as a "gothic shouting chamber."

He described London as the greatest city on earth.

With St Paul's Cathedral behind him, the MP said: "It is a city not just with so much potential but, of course, a city that his now in real danger: in danger from Brexit, from technological change, but above all I think in danger from what is happening in British politics; the kind of extremism that is taking over country."

The MP said that this is the most moderate  country on earth; one of the most settled places on earth, which treated people with civility and dignity.

He continued: "The reason I am going to be running in May to be Mayor London is that I believe the way to fight back is through this great city; through the traditions of compromise; the energy and diversity of this city; and to make it a better place...

"I'm leaving that gothic shouting chamber of Westminster; I'm getting away from a politics that makes me feel sometimes as though Trump has never left London; and I want to walk through every borough of this great city to get back to us on the ground."

He added that he wanted to bring about change through love, not division.

Earlier today, Mr Stewart told his constituents: "Being your Member of Parliament has been the privilege of my life. So much of what I love about Britain lies in Cumbria: our landscape, our farming communities, our deep history and the character of our people.

"I feel it every time I look out of the window at home in Butterwick. And I have felt it again and again since I first walked right around this constituency as a candidate. When I have thought of England, in my most difficult moments in Afghanistan or Iraq, I have thought of this place."

The MP added: "As for the future – I am a public servant to my core and will stay involved in politics, endeavouring to make my voice heard.

"I will, of course, continue to explain why I voted for a Brexit deal, while rejecting a No-Deal Brexit (especially because of the damage it would inflict on Cumbria and sectors such as farming).

"But ultimately I want to move beyond Brexit, and focus on getting things done on the ground. I think our great parties are now in danger of coming apart, and our great parliament is becoming increasingly diminished. I want to show how much difference can still be made outside parliament.

"So I hope to start work in another part of the country. I would like, if you will allow me, to remain closely involved with Cumbria – as a champion, supporting local charities and communities – not as your Member of Parliament, but I hope as your friend."

His departure comes just a day after he said he would resign if Boris Johnson got a Brexit deal with Brussels.

During his career, Mr Stewart has been prisons minister, and international development secretary.

He also stood as a candidate in the party's fiercely contested leadership election, accusing his pro-Brexit opponents of making unrealistic "unicorn" promises.

Earlier this week, Mr Stewart accused Mr Johnson's supporters of having a "blind faith" in him, and the Prime Minister of moving into a "Trumpian" universe, where he can break promises and not be affected.

The news triggered a spate of tributes from fellow MPs.

They included this tweet from Westmorland and Lonsdale MP Tim Farron: "This is a huge loss. Rory has been a strong voice for Cumbria and for decency, moderation and common sense."

Hereford MP Jesse Norman said: "A terrible pity. Rory Stewart [is] both wildly talented and a wonderfully decent human being."

Streatham MP Chuku Umunna wrote: "Very sad to hear this new. I remember when we both joined the Commons in 2010 attending our first PMQs together and [we were] both lamenting how awful it was - no change there. We haven’t agreed on everything but you are the kind of person the House needs more of not less."

Meanwhile, Robert Craig, president of the Penrith and The Border Conservative Association, said Mr Stewart would "possibly" not have made the decision if he still had the Tory whip. "I suppose had that changed... it seems to have become clear that that wasn't going to change and he has other ambitions," Mr Craig said.

He praised Mr Stewart as an "inspirational" MP who had managed to attract a broad church of followers, and criticised Mr Johnson for taking the party in an "extreme" direction.

The current Mayor of London is the former Labour MP Sadiq Khan, who took up office on 9 May 2016. He has repeatedly clashed with Donald Trump. The job was also once held by Ken Livingstone until he was defeated in May 2008 by Boris Johnson, who served two terms before being succeeded by Mr Khan.