Brexit: Labour seeking to block no deal
Labour has tabled a cross-party motion to try to stop a future prime minister pushing through a no-deal Brexit against the wishes of MPs.
The party is trying to force a vote to give MPs control of the timetable on 25 June and thereby the power to introduce legislation to avoid no deal.
Labour's Keir Starmer said it was a "safety valve", but Brexit Secretary Stephen Barclay criticised the plan.
Some Tory leadership hopefuls have said they would leave the EU without a deal.
Michael Gove said Labour's plans "must be resisted", as while he would prefer to agree a plan with the EU, "we must not rule out no deal."
For other candidates, including Rory Stewart and Mark Harper, the prospect of leaving without a deal is unacceptable.
However, neither man appears prepared to back the opposition motion. Mr Harper said his "instinct" was to oppose it while Mr Stewart - despite saying he was "wholly supportive" of the idea at his campaign launch in London - later tweeted that he would not be voting for it.
But Dominic Raab and Esther McVey have both said they would consider shutting down Parliament early - proroguing - in order to drive through no deal.
Leaving on a no-deal basis - without any agreement on the shape of the future relationship between the UK and EU - could lead to significant disruption.
The EU has previously said border checks would have to be brought in, affecting things like exports and travel and creating uncertainty around the rights of UK citizens living in the EU and vice-versa.
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The government normally controls business in the Commons - but MPs have previously seized control to legislate in favour of extending the Brexit process.
Labour's shadow Brexit secretary Sir Keir said the motion was a "safety valve" designed to ensure Parliament "cannot be locked out of the Brexit process" in the coming months.
It would allow Parliament to push back against a new prime minister "foolish enough" to pursue a no-deal Brexit without MPs' consent.
That was especially important, Sir Keir argued, because the Tory leadership contest had "become an arms race to promise the most damaging form of Brexit".
Mr Barclay, though, said the motion was a "blind motion" because it did not specify the legislation that would be introduced under its terms.
Labour had previously accused ministers of backing a "blind Brexit" because the future relationship was not spelled out in the withdrawal agreement - but this motion was guilty of the same approach, he said.
He argued it would be a "fundamental change" to the way the House operated and therefore should be opposed.
The motion has cross-party backing, including from one Tory MP - Sir Oliver Letwin - who is supporting Michael Gove in the leadership contest.
It has been signed by Jeremy Corbyn, SNP Westminster leader Ian Blackford, Lib Dem leader Sir Vince Cable, Change UK leader Anna Soubry, Plaid Cymru Westminster leader Liz Saville-Roberts and former Green Party leader Caroline Lucas.
Due to the confidence and supply agreement with the Democratic Unionist Party, the Tories have a majority in Parliament of five.
That means it would take only three Conservatives to vote with the Labour motion for it to pass - if all opposition party MPs back it.
Analysis: By Jonathan Blake, BBC political correspondent
Another attempt to re-write the rules, another heave in the procedural tug of war, another day of drama in Parliament. But will it work?
It's not a straight vote for or against a no-deal Brexit - that would not change the fact that it is written in law and agreed with the EU that Brexit will happen on 31 October.
Think of this plan not as a knockout blow in a boxing match, but the first of a complicated sequence of moves in a chess game.
Labour want to pull off something similar to what happened in March, when MPs took control of parliamentary time to force the government to request an extension to the Brexit process from the EU.
Step one is seizing control of business in the House of Commons, and that's clearly the plan this time around.
Beyond that, the details aren't clear.
Compelling the new prime minister to ask the EU to delay Brexit further is the most likely option. But the answer of course, might be "no".
Can Parliament stop a no-deal Brexit?
The default position in law is that the UK will leave the EU on 31 October - and if nothing changes, Brexit will happen regardless of whether there is a deal or not.
MPs wanting to stop a new PM leaving without a deal do however have a number of options at their disposal.
One would be to pass legislation requiring the government to seek an extension to the UK's membership. The EU would have to agree to an extension for it to be granted.
However, this would first require MPs to seize control of the parliamentary agenda, as Labour is attempting.
Another would be to use a vote of no confidence to bring down a government committed to pursuing a no-deal exit.
MPs could also use motions or political pressure to try and force the government into changing course.
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