The BBC's Vicki Young says she has been told by a minister that Theresa May will have to clarify what her "intention" not to lead the party into the next general election means in practice.

Our chief political correspondent says the normally loyal MP told her that the party needed a sense of how long the PM was going to stay in post.

Mrs May did not set a firm departure date during her speech to MPs earlier, leaving it somewhat open whether she was just going to see Brexit over the line or whether to she would stay longer to begin the process of negotiating the UK's future relationship with the EU.

One of the most prominent Conservative opponents of Brexit, Totnes MP Sarah Wollaston, tweeted a picture of her ballot paper to show she had voted for Theresa May.

Earlier in the day, Dr Wollaston made clear she was hoping the ballot would put an end to the disruption caused by the European Research Group of eurosceptic Tories.

She said: "I hope the ERG lose badly and we can see the back of their pompous threats for a year."

BBC Radio 5 live

Times columnist and former Conservative MP Matthew Parris says the European Research Group (ERG) have made a "great mistake" in "breaking cover quite so early".

He says they should have "left it until after the meaningful vote".

"The light has finally shone on how many of them there are. They’ve come out of their box. While they were in the box, nobody quite knew how many people there were. After tonight people will know that they are not as many as they thought."

Click here to listen live.

Bernard Jenkin, one of those MPs voting to get rid of Theresa May, says a different leader would have "very much stronger" authority.

He also tells the BBC that a change at the top would alter the parliamentary arithmetic when it came to Brexit, without going into much more detail.

He rejects suggestions that Brexiteers have chosen the wrong moment to try and oust the prime minister.

While acknowledging there is never a good time to, as he puts it, "refuel your administration in flight" he points out that the UK changed prime ministers while it was at war in 1940, when Winston Churchill replaced Neville Chamberlain in Downing Street.

Former Brexit Secretary David Davis said he was going to decide which way to vote after listening to Theresa May speak.

He is remaining just as tight-lipped as before, declining to answer journalists' questions as he came out of Committee Room 14.

Foreign Secretary Jeremy Hunt is among other big names to have cast their ballots in the last few minutes.

He has made it clear he is supporting the prime minister.

Image source, Conservative Party

Defence minister Tobias Ellwood has compared MPs who have forced the confidence vote to the right-wing Tea Party movement in the US.

Speaking outside Parliament, the Bournemouth East MP said the prime minister would survive the ballot and would "become stronger from it".

"What this has exposed is a group, a Tea Party if you like, a caucus that is determined to hijack where Brexit is going and they will be found out."

The group do not represent the views "of the party I joined", he said.

Mr Ellwood added that while the prime minister "won't be in No 10 forever" now is not the right time to choose a new leader.

Sky News

Health Secretary Matt Hancock says he is not in the business of making predictions but he "fully expects" the prime minister to win.

"A win's a win. She needs to win by one," he tells Sky News, while of course hoping for a somewhat wider margin of victory.

If that's the outcome, he says the PM should get straight back into the Brexit negotiations, with the aim of getting "assurances and changes" to the existing agreement.

Laura Kuenssberg
BBC political editor

Image source, AFP

Theresa May has addressed Conservative MPs in a meeting shortly before they began casting their ballots in a vote of confidence in her being their party leader.

As the prime minister arrived, her colleagues weren't quite sure of the result.

One member of the government told me the result of the ballot would be closer than expected - not a comfortable victory.

Another member of the cabinet told me it would change nothing - it was an exercise in futility.

Expectation right now is that she will win. But the prime minister has said that she'll go - though not just yet.

She'll have, what a loyal minister described as a "little more time". But to do quite what?

Tory rules say that if she wins tonight, she can stay on, undisturbed for another 12 months.

That takes one uncertainty off the table. But she is weaker - lonelier - with less authority to drive her Brexit compromise through.

Already cabinet ministers are speculating about which way she can tack.

The parliamentary sums don't change on her current planned agreement with the EU. The cabinet, let alone the rest of the Commons, won't give their backing.

So the prime minister is left tonight even with a likely victory, with less time in office, less authority, and with no credible Brexit policy - and now, even more to do.

Defence Secretary Gavin Williamson posted a picture of journalists outside the room as the PM addressed the 1922 Committee meeting shortly before voting started.

Image source, House of Commons

Former attorney general Dominic Grieve, who supports another Brexit referendum, says the PM has his support and the confidence vote "serves no purpose whatsoever".

However, he tells the BBC that he is doubtful that Theresa May will win any fresh concessions from the EU in the next couple of days.

If that is the case, he says the PM should put the agreement as it stands to the Commons before Christmas so that, should MPs reject it, the process of deciding what to do next can start as soon as possible.

Tory MP Marcus Fysh says he was not convinced by Theresa May's speech just now.

He tells the BBC she did not put forward any new plan for Brexit, merely expressing a "feeling" that MPs would be consulted more.

"It is very difficult to support her," he tells BBC News. "She did not really come up with anything new".

Mrs May would struggle to command the confidence of the House, he says, and if a snap election was called with Mrs May as leader he says a lot of Tory MPs in marginal seats would be out of a job.

He rejects claims that there is not enough time for a leadership contest before Brexit, saying the process can be "compressed" so that someone new is in place to renegotiate the existing agreement.