Prime minister urges MPs to give her plan a second look on eve of crunch vote on withdrawal agreement

Theresa May appears to be on course for a crushing defeat in the House of Commons as Britain’s bitterly divided MPs prepare to give their verdict on her Brexit deal in the “meaningful vote” on Tuesday.

With Downing Street all but resigned to losing by a significant margin, Guardian analysis pointed to a majority of more than 200 MPs against the prime minister.

Labour sources said that unless May made major unexpected concessions, any substantial margin against her would lead Jeremy Corbyn to call for a vote of no confidence in the government – perhaps as soon as Tuesday night. But since Conservative MPs are unlikely to offer Corbyn the backing he would need to win a no-confidence vote, he would then come under intense pressure to swing Labour’s weight behind a second referendum.

Cabinet ministers have not yet been told how May plans to keep the Brexit process on track if her deal is defeated – and they remain split on how she should proceed. Leavers are convinced that the prime minister should return to Brussels and press for fresh concessions, while remainers hope she will seek a compromise with Labour.

On Monday, May issued one final call to parliament to back her, urging MPs to “take a second look” at her deal and stressing that it was the only option on the table that could deliver an “orderly” exit from the EU.

But there was little evidence of movement after her speech. Few MPs were convinced by clarifications of the withdrawal agreement included in an exchange of letters between the prime minister and the European commission president, Jean-Claude Juncker, published on Monday, which May conceded did not go as far as some MPs had hoped.

With defeat for May all but inevitable, backbenchers led by the former Tory minister Nick Boles were hoping to seize the agenda in parliament and force the government to seek a softer, Norway-style Brexit deal.

And on Monday the Commons Speaker, John Bercow, was forced to bat away questions from loyal Tory MPs suggesting he was willing to facilitate a backbench takeover. “I have no intention of taking lectures in doing right by parliament from people who have been conspicuous in denial of and, sometimes, contempt for it,” he said. “I will stand up for the rights of the Commons and I won’t be pushed around by agents of the executive.”

Quick guide What are the details of Theresa May's deal? Show Hide The border Perhaps the most contentious issue. In order to avoid a hard border on the island of Ireland, a backstop arrangement that keeps the UK in the customs union and requires Northern Ireland to follow single market rules would prevail until a free-trade agreement is reached that avoids such a frontier. The financial settlement The UK and EU negotiators have agreed the former should honour those commitments it made while a member of the bloc – finally settling on a figure of £39bn. Transition period The deal would secure a status quo transition period to negotiate the nature of the future relationship, and during which the UK could begin to make trade deals with third countries. Citizens' rights A fraught issue at the outset, an agreement was reached relatively quickly that would see the UK respect the rights of EU citizens who arrive before the end of the transition period, which could be in 2022, and vice versa. The future The document is accompanied by a political declaration that sketches out the future relationship between the two parties – focusing primarily on trade and security.

There is growing speculation at Westminster that whichever course May pursues, she will be forced to announce that she will ask the EU27 to extend article 50. The prime minister refused to rule out doing so categorically on Monday, saying only that she didn’t believe it should be necessary.

“We’re leaving on 29 March. I’ve been clear I don’t believe we should be extending article 50 and I don’t believe we should be having a second referendum,” May said. “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.”

There are increasing fears in Whitehall that time is running out to put in place all the complex legislation necessary either to implement the withdrawal agreement – or, conversely, to prepare for no deal.

Quick guide Commons Brexit vote – the day's timetable Show Hide 11.30am The Commons begins sitting. The first item is questions to Matt Hancock, the health secretary, and his ministerial team. These are meant to last 30 minutes but can run slightly over. Then the Labour MP Debbie Abrahams briefly introduces a private member’s bill on public sector supply chains under a 10-minute rule motion. After midday If there are no urgent questions or ministerial statements to delay proceedings, the final day of debate on Theresa May’s Brexit deal – officially known as section 13(1)(b) of the European Union (Withdrawal) Act 2018 – begins. It will be opened for the government by the attorney general, Geoffrey Cox. Before 7pm May will make a final closing speech for the government, appealing for support for her deal. From 7pm Voting begins. However, before the crucial vote, MPs must vote on the four amendments accepted by the Speaker. One amendment, tabled by the Tory Hugo Swire, has been accepted by the government. At some point between around 7.30pm to 9.30pm MPs finally vote on the deal, as amended.

May addressed MPs of her own party on Monday night at the backbench 1922 Committee. The prime minister gave no indication of any plan B in what was described as a low-key, reflective meeting, but urged her party to support her deal to ensure that Brexit goes ahead and to keep Corbyn out of No 10.

Nadhim Zahawi, a junior minister, said that Alistair Burt, a Foreign Office minister and remainer, had told MPs that he now accepted the result of the referendum and urged Brexiters in his party, who were on the winning side, to do the same.

Brexiters leaving the meeting said their minds had not been changed. Steve Baker said: “She skilfully engineered her speech to ensure there were laughs in all the right places by not mentioning the deal.”

Just four Labour MPs have declared publicly that they could vote for May’s Brexit deal: Ian Austin, John Mann, Jim Fitzpatrick and Kevin Barron.

Corbyn urged his MPs to hold their nerve, addressing a packed meeting of the parliamentary Labour party on the eve of the vote. The Labour leader said the prime minister had comprehensively failed to scare his MPs into voting for her deal. “Theresa May has attempted to blackmail Labour MPs to vote for her botched deal by threatening the country with the chaos of no deal,” he said. “I know from conversations with colleagues that this has failed. The Labour party will not be held to ransom.”

Corbyn said May would “only have herself to blame” for two years of negotiating with her divided cabinet and backbenchers, rather than opening dialogue with Brussels, trade unions, businesses and parliament. “The Tory party’s botched deal will be rejected by Parliament. We will then need an election to have the chance to vote for a government that can bring our people together and address the deep-seated issues facing our country,” he said.

A Labour source said MPs “won’t have to wait very long” for a confidence vote to be called but that would be the sole decision of Corbyn rather than the shadow cabinet. “Jeremy will choose the moment,” the source said. However, the source said that should the vote be lost, it would not mean an immediate endorsement to campaign for a second referendum.

“The composite identifies a public vote as one of the options; it doesn’t say it’s the preferred option or the default option. Obviously we will judge how to deal with the options and get the best result for the country on the basis of what happens in parliament,” the source said.

The meaningful vote on May's Brexit deal – what happens next? Read more

The Brexit select committee chair, Hilary Benn, was under pressure on Monday night to withdraw a no-deal amendment, tabled before Christmas, that some MPs feared could limit the scale of the government’s defeat.

Downing Street declined to say whether it could support an amendment tabled by the backbencher Andrew Murrison, chairman of the Northern Ireland select committee, aimed at putting a formal end date on the Irish backstop. Such a sunset clause would be likely to run into trouble in Brussels, with the EU27 adamant that the backstop must apply “unless and until” an alternative arrangement is in place that avoids the need for a hard border.

But the amendment’s supporters believe it will strengthen the PM’s hand if she returns to Brussels in search of fresh concessions after Tuesday. They also hope that if it passes, it could help limit the scale of the government defeat.

Governments have been defeated by a margin of more than 100 votes only three times in the last century, according to professor Philip Cowley, of Queen Mary University of London – all of those during the minority Labour administration of 1924.

The House of Lords had its own vote on the government’s Brexit deal on Monday evening, rejecting it by a thumping 321 votes to 152 – a majority of 169. Labour’s leader in the Lords, Angela Smith, called it “a vote for common sense”.

• This article was amended on 16 January 2019 because an earlier version referred to Jean-Claude Juncker as the EU council’s president. Juncker is president of the European commission.