Theresa May has made a desperate last-ditch plea begging her own MPs to back her Brexit plans in the face of an expected historic defeat.

The prime minister beseeched Conservative MPs at a closed meeting to think of the future of their party and compromise, with around 100 of them considering voting against her.

But Brexiteers still left the meeting determined to reject her plans, while Ms May also now faces up to 12 separate attempts from rebel and opposition MPs to re-shape her strategy before the final vote on Tuesday.

She gave no indication as to her course of action if she loses, but Labour’s Jeremy Corbyn spoke to his own MPs in a room nearby restating his determination to call a motion of no confidence and trigger an election.

After 19 months of negotiation, a dozen EU summits and countless hours taking questions at the despatch box, Ms May will finally put her Brexit deal to a vote of the Commons on Tuesday.

With her final chance to address all MPs coming shortly before the vote due after 7pm, she held a private gathering of Tories on Monday night to try to win over rebels.

Those inside said the prime minister had urged them to think in the “long term” and be pragmatic. She said the Conservatives had always been successful because they had been willing to compromise.

She warned again, as she and other ministers have done before, how difficult achieving a no-deal Brexit will be and how damaging it could be to Britain.

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Minister Nadhim Zahawi said she had told them they needed to deliver on Brexit and prevent a Labour government.

“She said we have got to keep Jeremy Corbyn as far away as possible from No 10,” he said. “To do that, we have got to come together.”

Among those who backed her message were foreign office minister Alistair Burt who told Brexiteers in the room to “accept the fact that they have won” and “to bank that and move on to the next stage”.

Solicitor general Robert Buckland said the meeting was in a “sombre, reflective” mood, but key figures in the European Research Group, Steve Baker and Mark Francois, left indicating that Ms May’s appeal had fallen on deaf ears.

Much of the opposition to her deal to focuses on the hated “Irish backstop”, which would come into play if no future trading arrangement is in place by December 2020, and could keep the UK in a customs union indefinitely.

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Earlier in the day, Andrew Murrison MP tabled an amendment to the Brexit motion to create a “sunset clause” preventing the backstop extending beyond the end of 2021.

It was one of a series of amendments that speaker John Bercow could call to be voted on ahead of the main vote on Tuesday. Others include an aim to secure a new referendum and block a no-deal Brexit.

Downing Street are said to be supportive of the Murrison plan but have not explicitly said so, with some ministers having suggested that if it is passed, it would give Ms May an opportunity to return to Brussels with a mandate for further renegotiation.

On Monday, Ms May set out the details of assurances given in a joint letter from Donald Tusk and Jean-Claude Juncker over the hated “Irish backstop”’, which is preventing so many of her MPs from supporting her deal.

She said she knew some MPs wanted a mechanism to allow the UK to decide unilaterally to exit the backstop or a time limit to the arrangement.

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But she added: “The EU would not agree to this, because they fear such a provision could allow the UK to leave the backstop at any time without any wider agreements in place and require a hard border to be erected between Northern Ireland and Ireland.”

Ms May said the letter made clear that if her deal was approved in the Commons on Tuesday, talks on a future relationship agreement could start immediately.

Labour leader Mr Corbyn said Ms May has “completely and utterly failed” to allay MPs’ concerns about her Brexit deal.

Mr Corbyn, speaking in the Commons, said letters from the EU and the prime minister over the Irish backstop were “nothing more than a repetition of exactly the same position that was pulled more than one month ago”.

He said: “It categorically does not give the legal assurances this House was promised and contains nothing but warm words and aspirations.”

On Monday night, Ms May’s deal suffered its first official parliamentary defeat in the House of Lords as peers voted by 321 votes to 152 to reject it.

With the majority of 169, peers backed an opposition motion warning the deal would damage the UK’s economic prosperity, internal security and global influence.