Mr Raab said that if that happened, it was essential she ordered Tory MPs to vote to leave open the option of a no-deal break.
Pro-Brexit protesters demonstrate outside 10 Downing St. on Saturday as the chances of Britain leaving the European Union hang in the balance with a parliamentary vote scheduled for Tuesday. Or, she added, Britain could leave without a deal to soften the shock, a nightmare scenario for many companies.
If her deal is rejected, lawmakers will be able to vote on Wednesday and Thursday on whether they want to leave the bloc without a deal or ask for a delay to Brexit beyond March 29 - all but wresting control of Brexit from the government.
If lawmakers reject May's deal on Tuesday, she has promised to let them vote the next day on whether to leave without a deal on March 29.
But in a sign ministers are preparing to go back to the Commons on Tuesday without fresh concessions, Chancellor Philip Hammond said such fears about the backstop were overblown. "I certainly see myself as a guardian of Brexit and I'm absolutely determined to make sure that we deliver on the decision by the United Kingdom".
At the heart of the House of Commons's opposition to the already-negotiated divorce deal is the so-called "backstop", a provision to keep the sensitive Irish border open after Brexit, which the eurosceptic wing of Mrs May's Conservative party fears could trap the United Kingdom in the EU's trading rules forever.
But despite the war of words, both sides say talks are continuing over the weekend, just days before May will face parliament once again after resoundingly losing the first vote in parliament on January 15. May relies on DUP votes to get her legislation passed after she lost her parliamentary majority.
But, May's attempts to get the clause rewritten have so far failed to yield any result, with European Union negotiators unwilling to meet her demands, and Britain rejecting a compromise offer. "How can a government function that doesn't keep its promises?" he told Sky News's Sophy Ridge on Sunday programme.
Sir Keir said he expected there would still be an opportunity for MPs to vote for a second referendum in the days ahead, either on a Labour amendment or one tabled by backbenchers.
Amid the political chaos, many company chiefs are aghast at London's handling of Brexit and say it has already damaged Britain's reputation as Europe's pre-eminent destination for foreign investment.
"There is a risk and a possibility that we end up losing Brexit if we get the votes wrong in the next couple of weeks". "Those carrying additional inventory know an extension will squeeze their cashflow for longer".