MPs are debating eight proposals on the future of Brexit ahead of votes later on a way forward.
It comes after MPs took control of the House from the government as they attempt to find a majority for the next steps in the Brexit process.
Measures being debated include leaving without a deal, forming a customs union and a confirmatory referendum.
Theresa May is still trying to drum up support for her deal, despite it being voted down by a large margin twice.
But after the Speaker of the House, John Bercow, announced which eight proposals he had chosen for votes, he reiterated his earlier warnings that the PM's deal could not come back for a vote if it had not significantly changed.
The prime minister is preparing to meet her backbenchers later at the Conservative 1922 committee to push for further support for her withdrawal agreement
Earlier, the government ordered their MPs to vote against a business motion securing the indicative votes for this evening, but lost by 331 to 287.
Conservative backbencher Sir Oliver Letwin, whose cross-party proposal ushered in today's debate, said the only way leaving the EU with no-deal can be prevented is by crystallising an alternative majority and trying to carry it forward.
He said that if MPs supported the prime minister's deal in another meaningful vote this would be "the easy route".
But he added that he "profoundly hopes" that if on Monday there is a majority view in favour of a particular position, that the government will say that it will carry that forward.