Laura Kuenssberg
BBC political editor

Looking nervous but entirely determined, the prime minister's message this morning won't surprise anyone who knows her well - she will fight the challenge to her leadership with everything she has.

But all the doubts, all the anxieties, all the unhappiness about the prime minister's leadership that have crystallised around the conundrum of Brexit have finally come to a head.

Her party - not the opposition, not Parliament - deciding that her time may be up.

But the prime minister that promised she would be strong and stable is instead at the top of a party that looks weak and chaotic at a vital time.

Read more from Laura here.

BBC Radio 5 live

BBC Radio 5 live is asking listeners if they are 'backing Theresa May?'

David in North Yorkshire says: "I'm over the edge. This is just getting beyond a joke. The ramifications of this for me personally are that I now can't vote Conservative in the future because I can never forgive them for doing this.

"And I don’t want to vote Labour either.

"So I’m now done with politics and politicians. I’m bereft, I’m a political orphan, I can’t vote for anyone.

"The damage that these guys and girls are doing to this country is horrendous."

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Today Programme
BBC Radio 4

Health Secretary Matt Hancock told BBC Radio 4's Today programme the prime minister's statement was "characteristically strong".

He said: "Winning by one vote is all she needs, but crucially I hope she wins by far, far more than that because I feel so strongly that the nation needs to be behind our leader in order to get the very best deal."

Mr Hancock questioned whether any other possible candidate could unite the party if there was a leadership contest.

"It’s not like there’s anybody else who has a consensus behind them," he said.

BBC News Channel

MP Bill Cash says he thinks a leadership contest is "necessary" for his party.

The Tory backbencher tells BBC News: "It is quite clear that the House of Commons won't accept the withdrawal agreement.

"It's extremely defective in a whole range of areas. It is not in the national interest.

"The reality is that the DUP will not support the prime minister in relation to the withdrawal agreement, and that means that indefinitely under those circumstances we would not have a majority in the House of Commons."

Asked if it was in the national interest for there to be "less certainty" in the UK, he adds: "You can't get less certainty than not having a withdrawal agreement of any description.

"The reality is we need to have a renegotiation."

Ian Lavery MP, chair of the Labour Party, says:

“With only weeks left before Britain leaves the EU, Theresa May’s weakness and failure has completely immobilised the government at this critical time for the country.

“The prime minister’s half-baked Brexit deal does not have the backing of her Cabinet, her party, Parliament or the country.

“The Conservative Party’s internal divisions are putting people’s jobs and living standards at risk.”

Image source, Getty Images

Anna Soubry says she is "embarrassed" to be a member of her party today.

Speaking at an event run by the Institute for Government, the Tory Remainer says: “Today I sit before you having been embarrassed to have been an MP on Monday.

"I’m now embarrassed to be a Conservative.”

BBC News Channel

Tory MP Owen Paterson has stood by his decision to put in a letter calling for a confidence vote in Theresa May.

"People like me thought long and hard, and delayed [putting in a letter]," he tells the BBC.

"But it just led to exasperation at the end and she was determined to follow the wrong course.

"She is sadly determined to stick to her deal which is not going to get through the House of Commons, and worse, if it did get through the House of Commons, she would lose the support of the DUP which triggers a general election."

Mr Paterson says it is "perfectly possible" his fellow Tories will rally round Mrs May and secure her leadership.

But he points out that some "17.4 million people voted to leave, and in the general election our manifesto was very clear - leave would be interpreted by leaving the single market, leaving the customs union and leaving the remit of the ECJ".

He adds: "That is what we were all elected on, that is what all our supporters in the country still support.

"We are in tune with the mainstream of our party, we are manifesto Conservatives."

BBC Radio 5 live

Nick Boles, who has backed a Norway-style deal, criticised the role of the Brexit-supporting European Research Group in bringing about the no confidence ballot.

Speaking outside No 10, Theresa May said: "A leadership election would not change the fundamentals of the negotiation or the parliamentary arithmetic.

"Weeks spent tearing ourselves apart will only create more division just as we should be standing together to serve our country."

Mrs May was due to go to Dublin today to meet with Leo Varadkar to discuss her Brexit deal.

But she says she has cancelled the trip to make the case for her leadership.

"I stand ready to finish the job," she adds.