Neu product manager Richard Phillips-Kerr said: "The government and party whips are compelling MPs to vote 'on behalf of their constituents" when considering the PM's deal. Lawmakers would earn the "undying contempt" of the British people if they reject it, he said.
Shadow home secretary Diane Abbot said: "On the question of security, assertions, aspirations, a wish list is not enough, we need a treaty". "In turn, that would mean the most damaging uncertainty economically".
A group of lawmakers who want a more definitive break from the European Union than envisaged by May's plan said the government had invited senior lawmakers to a briefing on Thursday at its emergency planning body on the impact of a no-deal Brexit.
Asked if Mrs May still felt she could command a majority in the Commons for the crunch vote next Tuesday, a Downing Street source said: "Everybody knows the parliamentary arithmetic". "The idea that there's a better deal to be negotiated at the 11th hour is a delusion".
May replied that she had always been clear about the implications of the deal's provisions on Northern Ireland, which risk keeping Britain tied to the EU's economic rules for years after leaving next March. Britain would be the only advanced economy trading on WTO terms, Hammond says. Even if we get a deal next week the issue is far from over - it is just Act One.
The poll comes after the prime minister last month delivered the three option ultimatum to her MPs: her deal, no deal or no Brexit.
Pro-EU legislators say the amendment makes the prospect of a "no-deal" Brexit less likely, because Parliament can direct the government to take that option off the table.
"The risk is that we end up with no Brexit at all".
DUP leader Nigel Dodds said his party would vote against the deal, but would not move to bring down May's government.
"The only way to resolve this is to go back to the people", he said.
One potential measure reportedly being floated as a way to win over would-be rebels is a "parliamentary lock" which would give MPs a vote before the Northern Irish backstop is implemented.
"There are questions about how decisions are taken as to whether we go into the backstop, because that isn't an automatic", May said.
Many want to see the government lose on Tuesday.
"On that basis, while acknowledging the narrowness of the national result, I voted to allow the May Government to proceed with negotiating our withdrawal from the EU. We are ready to support them".
European Union diplomats said unless there is a quick fix and a swift and successful second vote in the British parliament, the case would drag on into 2019, increasing pressure on all sides.
The UK would also not be able to leave the backstop without European Union agreement.
But he admitted: "I don't think there's any point in ploughing ahead and losing the vote heavily". But he says the next step isn't a general election, which he reckons is "most unlikely".
May's chances of survival were dealt a blow on Tuesday when her government suffered a humbling hat-trick of defeats in the Commons over Brexit legal advice.
The contempt vote forced the release of the attorney general's advice Wednesday, and the document did little to reassure members of Parliament of the merits of Prime Minister Theresa May's deal with Brussels.
And in another development, the European Court of Justice said it would deliver a ruling on Monday on whether the United Kingdom could unilaterally cancel Brexit by reversing Article 50 - the day before the MPs' crunch vote.