MPs are voting on a bill that would require the PM to seek an extension to Article 50
The PM and Jeremy Corbyn met for two hours this afternoon to discuss Brexit
Downing Street called the talks "constructive"
Mr Corbyn called them "useful but inconclusive"
Mrs May also met the first ministers of Scotland and Wales, Nicola Sturgeon and Mark Drakeford
Brexit minister Chris Heaton-Harris quits role in protest at Mrs May ruling out no-deal Brexit
Earlier, minister Nigel Adams resigned over PM's decision to meet Mr Corbyn for talks
A vote on whether MPs could seize control of the parliamentary timetable on Monday was tied, before the speaker rejected it with his casting vote
Business of the House motion
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"it is because the government has lost the confidence of the House that this motion is before us," says Lib Dem Tom Brake.
He says that after 1,012 days the government has "failed to find a solution".
"This is day two of Parliament's attempt to find a cross-party solution to the Brexit dilemma," he says.
"I hope we will be successful."
Business of the House motion
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Image source, HoC"To overturn the business of the House rules under this business motion seems to be utterly perverse," says Conservative Bill Cash.
"The reason why government business takes precedence is because of democracy.
"These indicative votes are like liquorice allsorts - or rather humbugs."
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Image source, HoC"We are on the cusp of the government losing control," says Conservative Edward Leigh.
"We are facing permanent membership of the customs union which runs contrary to our manifesto," he warns his fellow MPs.
"We have to get real.
"I would rather vote for the prime minister's deal, which at least delivers some sort of Brexit."
A petition calling for the UK to stay in the EU, which has amassed more than six million signatures, is due to be debated in Westminster Hall from 16:30 BST.
The petition, demanding Article 50 be revoked, is the most popular since Parliament's petition website launched.
Two others will also be discussed. One, demanding a new referendum, has over 180,000 signatures. The other, urging MPs to "honour the referendum result", has more than 170,000.
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Image source, HoCLabour MP Angela Eagle notes Andrea Leadsom's opposition to MPs debating their own Brexit proposals.
She argues that MPs "are close to reaching some conclusions".
"It is almost like the Leader of the House doesn't want us to reach a conclusion so she can try to have a meaningful vote four, five, six, seven, eight, nine and, God forgive us, even 10," she says.
Nick Eardley
BBC political correspondent
International Trade Secretary Liam Fox tells the BBC joining a customs union would be a “betrayal of Brexit”.
He says the UK would have to follow rules set by the EU – which could mean Brussels demanding access to UK markets “whether or not we wanted it”.
“It’s time we went back to a proper Brexit,” he says.
Mr Fox refuses to be drawn on whether he would stay in government if membership of a customs union becomes official policy.
Image source, Getty ImagesA British MEP has been removed from his role overseeing the European Parliament’s work on legislation to ensure British visitors don’t need a visa to visit the EU if there’s a no-deal Brexit.
Claude Moraes had strenuously opposed the inclusion of a footnote in the legislation that described Gibraltar as a “colony of the crown".
He was removed from his role today by a committee of senior MEPs following complaints from the Spanish government. The move was approved by the centre-right and centre-left but opposed by the other political groups in the Parliament.
“It was brutal,” Mr Moraes said after the decision was made this afternoon.
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Image source, HoCLeader of the House Andrea Leadsom opens the debate by telling MPs that the Business of the House motion "sets an extremely concerning precedent for democracy".
She goes on to say that the indicative votes last week demonstrated that "there is no agreed way forward".
She says the prime minister's deal remains the best one on offer.
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Before starting to debate MPs' Brexit proposals, the politicians must first agree to the Business of the House motion.
The motion sets out the framework for the debate as well as setting aside time on Wednesday for MPs to take control of the timetable again.
Labour MP Gareth Snell had tabled an amendment to the motion trying to cancel Wednesday's plans - however it has not been selected by the Speaker John Bercow.
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Image source, HoCHome Office questions ends and Conservative Richard Drax rises to make a point of order.
He tells MPs he has "not been true to himself".
He explains that "although doing what I believed to be in the country's best interest" by voting for the prime minister's withdrawal plan, "what I should have done- and did not do - was trust my instincts and trust the British people."
He says he made "the wrong call" and apologises to other MPs.
"The withdrawal agreement as it stands should never see the light of day again," he says.
He adds that if the prime minister cannot take the UK out of the EU on 12 April "she must resign immediately".
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Image source, Getty ImagesWith all the speculation about the various options that are gaining support, it is worth noting that the government is expected to whip against the business motion enabling the whole indicative vote process to go ahead.
However, it is expected to pass.
Conservative MPs are then set to be given a free vote - although it is understood Cabinet ministers are being told to abstain.
BBC assistant political editor Norman Smith says if MPs do not settle on a favoured option this evening, Theresa May could bring back her deal to the Commons for the fourth time.
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Shadow foreign secretary Emily Thornberry has been speaking on the BBC News channel.
She says the issue of freedom of movement means the party is not “comfortable” with the idea of being in the single market.
“We’ve said throughout, for the last couple of years, it’s difficult for us to be in the single market.”
But “we’re trying to find a compromise” she says, “so therefore we will be voting for things which are broadly in line with our new policy, even things that are not exactly in line with our policy".
The Common Market 2.0 option is “going to be better than Theresa May’s deal, and certainly better than no deal, so we will be voting for that," she says.
MPs rejected Theresa May's Brexit deal for a third time last week. The government lost by 344 votes to 286, a majority of 58.
But on this occasion there was a key difference: MPs only voted on the withdrawal agreement and not the political declaration. Previously, both of these were voted on and rejected.
So, what are they?
Katya Adler
Europe Editor
Image source, Getty ImagesIn Berlin on Sunday, demonstrators held aloft EU and UK flags - and the German word for "friends"
The EU is closely watching the indicative votes process in the UK parliament today.
EU leaders would, of course, welcome a softer Brexit. It would ease friction in post-Brexit EU-UK trade relations – but at the same time, they believe MPs are out of touch with reality.
However many Brexit options are voted on today in the House of Commons, EU law stipulates that there are only three on the table: no deal, no Brexit, or Theresa May's negotiated deal.