May pledges to go back to Brussels If and when she loses the vote on her deal, under existing legislation Mrs May is required to come back to parliament within three days to set out how the government intends to proceed and lay a motion before the house, one that can be amended by MPs.
The speech was overshadowed on Monday morning by an embarrassing gaffe in the key section of her final plea to MPs, which said MPs had always respected the vote in previous referendums including ones where there was a much narrower margin such as the creation of the Welsh assembly.
She is expected to do that soon - if not immediately - after the defeat.
It also gives Parliament more control over Brexit.
Speaker John Bercow sparked uproar in the Commons last week after he selected an amendment from Tory former minister Dominic Grieve which attempts to speed up the process for the Government to reveal what it will do next if the PM's Brexit deal is rejected.More news: China's foreign trade hits historic high in 2018
"We have an instruction from the British people to leave and it's our duty to deliver on that but I want to do it in a way that is smooth and orderly and protects jobs and security".
"What if we found ourselves in a situation where parliament tried to take the United Kingdom out of the European Union in opposition to a remain vote?"
"I hope my colleagues will listen to those and recognise the best way forward is to support the Government's agreement because it delivers on the referendum result and does so in a way that minimises the risks to our economy". European Union officials earlier warned that a letter of assurances from Jean-Claude Juncker and Donald Tusk on the Irish backstop, due to be unveiled on Monday in the Commons, contained nothing new.
"I would not stay in office, I would stand in front of that no deal juggernaut", he told BBC Radio 4′s Westminster Hour.
'It would be an irresponsible act of self-harm and from security reasons alone it would be damaging our worldwide reputation as well.More news: DRC: Fayulu supporters dispersed by riot police at court
May's government suffered a string of resignations in November after the prime minister announced that her cabinet had settled on a Brexit deal.
Backbenchers Sir Edward Leigh, Sir Geoffrey Clifton-Brown, Andrew Murrison and Caroline Johnson expressed reservations at backing the deal, but each said they had come to the conclusion to support it.
The EIU said that the two most likely outcomes, following the downgrade of the likelihood that a no-deal Brexit would happen, is that there is either "an eventual approval of the Brexit deal, or a second referendum".
"I think MPs need to act with a bit of humility here because we had the same vote as everybody else in that referendum", he said.
According to the Sunday Times, the Government's chief whip Julian Smith briefed Mrs May on Friday after commissioning legal advice that said: "Without control over the order paper... the Government would lose its ability to govern".More news: Concept This Is Cadillac's New Electric Crossover
He said: "Clearly if Theresa May's deal is voted down, clearly if a general election takes place and a Labour government comes in - an election would take place February, March time - clearly there's only a few weeks between that and the leave date, there would have to be time for those negotiations".