Theresa May has warned Tory rebels they risk a Jeremy Corbyn government and the break-up of the UK if they reject her Brexit deal in tonight's crunch vote.
Allies of the Prime Minister acknowledged her plans could be rejected by a majority approaching 200 votes – eclipsing record government defeats of modern times.
They believe Labour leader Jeremy Corbyn will then try to exploit Tory divisions by forcing a formal vote of no confidence in the Government tonight, which could usher in a general election.
Allies of Mrs May last night indicated she would tell MPs that she will continue to pursue her deal even if it is heavily defeated.
She acknowledged that the plan was not perfect, but added: 'When the history books are written, people will look at the decision of this House tomorrow and ask: Did we deliver on the country's vote to leave the European Union?'
The PM made her stark warnings in a last-ditch bid to drum up some desperately needed support from her backbenchers in the last 24 hours before the historic vote.
She said the thorny issue of Brexit has divided the Tories for the many years she has been in politics - hinting that her deal could finally put the issue to rest.
And she warned the SNP will seize on any Brexit disarray to demand another referendum on Scottish independence.
Mrs May told MPs: 'We have to deliver Brexit – it is the instruction the British people gave us.'
The deal suffered its first official parliamentary defeat last night in the Lords, as peers registered their symbolic opposition to it by 321 votes to 152.
Mrs May's eleventh-hour plea came shortly after Treasury minister Mel Stride was pictured leaving Downing Street clutching a sheet of paper bearing the words 'No food. No Channel tunnel'.
ERG chairman Jacob Rees-Mogg said he expected 'a cascade' of MPs voting against the deal.
The North Somerset Conservative said: 'I think there will be a cascade of people going into the lobbies against this bad deal because it denies us the opportunities that will make Brexit a success.
'Instead we're tied into a protectionist racket that keeps prices high and makes our economy less efficient, that means the rest of the world is overtaking us and the whole of Europe because it becomes less competitive as it seeks an outmoded, anti-competitive system thinking it can simply protect itself.
'We risk denying ourselves these extraordinary opportunities and in doing so taking ourselves away from the electorate who we promised to deliver on Brexit for.'
Asked by his MPs when he would bring the challenge – which could lead to a general election – Labour's leader said it was 'coming soon'.
Shadow chancellor John McDonnell reiterated his party's desire for a general election but added MPs may want a 'public vote' on a new deal backed by Parliament if this does not take place.
e said: 'Tomorrow this deal will go down, so it's time now to put the mistakes of the past two years behind us, clear away the debris of this deal and the debris of this Government's failed negotiations.
'It's clear to me, to break the deadlock and deliver a clear mandate for that new approach, I believe we need a general election. It's a time to let the people have their say.'
Speaking after Mrs May met with Tory MPs, Education Minister Nadhim Zahawi said Mrs May also warned of the economic dangers of a no deal Brexit.
He said: 'She wanted to focus minds that we must deliver Brexit and to keep Jeremy Corbyn as far away from Number 10 as possible, and to do that we have to hang together.
'And she pointed out that no deal would be a threat to the union with the SNP pushing for a second referendum.'
Mr Zahawi said she the PM was 'relaxed' as she addressed her backbenchers in Portcullis House last night.
He said: 'She was very relaxed and cracked a few jokes. It was one of her best performances.
'The room was focused and listening and absorbing and very reflective about what the realpolitik was.'
The PM also warned Tory MPs that business is desperate for the to get a Brexit deal and have warned of the risk to jobs and investment if they crash out of the EU.
And in a rare move, Mrs May spoke personally about how the bitter EU debate has divided the Conservative Party for many years.
Mr Zahawi said: 'She talked about her career in Parliament and how divisive the European issue has been for the country and of course the Conservative Party.'
But Brexiteers who were in the meeting were less than impressed and many left early.
Tory MP and Brexiteer Mark Francois left early and said he thinks her deal will still be rejected by Tory MPs in the crunch vote in 24 hours time.
A Tory minister was earlier accused of stunting up a picture showing his notes apparently predicting the dire consequences of a no-deal Brexit.
Treasury minister Mel Stride was pictured leaving Downing Street clutching a sheet of paper bearing the words 'No food. No Channel tunnel'.
It led critics to claim Mr Stride had deliberately exposed his notes as part of a scare campaign to get MPs to vote for Theresa May's Brexit deal, while his allies insisted they were points of discussion - not warnings in themselves.
Earlier Mrs May warned MPs that 'history' will judge them if they kill off her Brexit deal - as she insisted she has won new concessions from the EU.
In a desperate last-ditch plea in the Commons, the Prime Minister said in future people would look back and ask whether politicians had 'delivered' on the verdict of the referendum.
Mrs May hailed the latest 'assurances' from Brussels, saying they showed the UK would not be trapped in the Irish border backstop - although she also conceded she had not secured everything she hoped for.
The impassioned appeal came after a frantically grueling day in which Mrs May gave a Brexit speech in Stoke-on-Trent, before returning to London to face MPs for hours in the Commons. Later she is due to address Tory backbenchers and peers in what promises to be another pressure-cooked session.
But as tensions reached boiling point with just 24 hours to go before a vote that could define the country's future, Mrs May suffer another resignation from her government - as a whip quit to oppose her deal.
Gareth Johnson said he was putting his 'loyalty to the country above loyalty to the government'.
There are fears that the resignation could open the floodgates - with several other ministers and whips thought to be on the brink.
Addressing MPs last night, Mrs May again urged them to recognise that a no-deal Brexit represented the 'real threat' to the unity of the UK, as it would fuel calls for Scottish independence.
And she cautioned Eurosceptics that killing off her package and trying to force through departure without any agreement could mean the country never leaves the bloc.
'When the history books are written, people will look at the decision of this House tomorrow and ask, did we deliver on the country's vote to leave the European Union?
'Did we safeguard our economy, our security and our Union? Or did we let the British people down?
'I say we should deliver for the British people and get on with building a brighter future for our country by backing this deal tomorrow.'
In his letter to Mrs May this afternoon, Mr Johnson said he believed the package thrashed out with Brussels would be 'detrimental to the national interest' and set Northern Ireland 'apart from the rest of the UK'.
'I have therefore decided the time has come to place my loyalty to my country above my loyalty to the government,' he wrote.
Government sources tried to play down the resignation - the 13th for Mrs May over Brexit - pointing out that Mr Johnson represents the heavily Leave-supporting Dartford constituency.
Earlier, Mrs May had appealed for Tory Eurosceptics to look at the mounting revolt by Remainers, and realise that Parliament is ready to block the country from crashing out.
In a speech in Leave-voting Stoke-on-Trent this morning, Mrs May said it was clear some politicians would use 'every device' to stop Brexit happening.
Underlining the dangers of the crisis wracking Westminster, she urged MPs to consider the 'consequences' of their actions for people's faith in democracy.
Mrs May also pointed to the letter from the EU chiefs, which insists the Irish border backstop - the most controversial part of the Brexit deal - will only be 'temporary'.
'We have secured valuable new clarifications and assurances,' Mrs May said, while admitting that the commitment 'did not go as far' as some MPs wanted.
Despite her scramble, Mrs May looks to be on track for a catastrophic defeat - with frantic manoeuvring under way over what happens next.
A dozen Tory former ministers including Boris Johnson have urged wavering colleagues to stand firm against the deal, saying leaving on World Trade Organisation terms would not be a disaster.
In her speech, Mrs May said she now believes if her deal is defeated, MPs blocking Brexit is more likely than leaving without a deal.
She said failure to pass her package could mean crashing out - but there was a 'bigger risk' of not leaving the EU at all.
Mrs May rejected the idea that alternatives to her Withdrawal Agreement were available.
'Nobody has yet come up with an alternative Brexit deal that is negotiable and that delivers on the result of the referendum,' she said.
'The only deal on the table is the one MPs will vote on tomorrow night.
In a message to Remainer rebels, she said: 'You can take no deal off the table by voting for that deal. 'If no deal is as bad as you believe it is, it will be the height of recklessness to do anything else.'
Mrs May brushed aside suggestions that the EU might extend the two-year withdrawal process under Article 50 to the summer to allow more time for the UK to settle its position.
'We are leaving on March 29,' she said. 'I have been clear I don't believe we should be extending Article 50 and I don't believe we should be having a second referendum.'
Mrs May said the letters from the EU carried 'legal force' and 'make absolutely clear that the backstop is not a threat or a trap'.
She added: 'I fully understand that the new legal and political assurances which are contained in the letters from Donald Tusk and Jean-Claude Juncker do not go as far as some MPs would like.
'But I'm convinced that MPs now have the clearest assurances that this is the best deal possible and is worthy of their support.'
The PM again ruled out a permanent customs union with the EU - floated by some MPs as a potential compromise that could command a Parliamentary majority.
'I have always been clear that we will not be in the customs union, because being in the customs union has with it other aspects which are not what people voted for,' she said.
Mrs May also offered an olive branch to Labour MPs who might consider backing her deal with an appeal over workers' rights and environmental standards.
She said: 'I could not have been clearer that far from wanting to see a reduction in our standards in these areas, the UK will instead continue to be a world leader.
'We have committed to addressing these concerns and will work with MPs from across the house on how best to implement them, looking at legislation where necessary to deliver the best possible results for workers across the UK.'
Mrs May added that while no-deal remained a serious risk, 'having observed events at Westminster over the last seven days it is now my judgment that the likely outcome is a paralysis in Parliament that risks there being no Brexit'.
It emerged over the weekend that Remainers from across parties are plotting an extraordinary bid to seize control from the government if it tries to push ahead with a no-deal
Brexit. Conservative MP Nick Boles today confirmed plans to tear up Commons rules so MPs could propose legislation - something the government currently has power over.
Ministers fear Speaker John Bercow would help the rebellion. Last week he flouted procedural convention to select 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.
But the fledgling revolt was at risk of collapsing after it was dismissed by pro-EU MPs.
Senior Tory Sarah Wollaston, previously one of the most outspoken anti-Brexit rebels, said it would fly in the face of the constitution.
She pointed out that the Liaison Committee - on which she serves had no role in drafting legislation.
'Under our constitution, Parliament can either change the government's mind or change the government,' she said.
'It can propose legislation for government to take forward & it can amend or block it but back bench MPs cannot take over conducting a complex international negotiation.'
Asked during an LBC radio interview today what would happen, Mr Johnson said: 'I think the deal goes down.
'I think, possibly, some colleagues are being scared by this idea that there might be no Brexit as a result of voting it down.
'I think that's nonsense. Britain will leave in March, absolutely, and that's the bottom line.'
Mr Johnson said that defying the result of the referendum would be 'playing with fire'.
'If we think that by coming up with all sorts of complicated amendments and you know delaying tactics, we're gonna fool the British public, we're going to manage to frustrate Brexit, I think we will reap the whirlwind,' he said.
'People will feel betrayed and I think they will feel that there has been a great conspiracy by you know the deep state of the UK, the people who really run the country, to overturn the vote of the people.'
A dozen leading Brexiteers – including eight former members of Mrs May's Cabinet – have written to all Conservative MPs urging them to vote against the Prime Minister's deal.
In a joint letter sent to every Tory MP, former ministers including Boris Johnson, David Davis and Dominic Raab call upon Mrs May to stage one final attempt to persuade the EU to drop the Irish backstop which threatens to halt Britain's exit from the custom union indefinitely.
But if the EU fails to comply on agreeing such a deal, the Britain must 'have the confidence' to leave on World Trade Organisation (WTO) terms on March 29.
The letter is also signed by other former Cabinet members including Iain Duncan Smith, Esther McVey and Priti Patel.
They write: 'It is right to vote down this bad deal and that in doing so we will unlock a better future for our party, our country and its people.'
They add: 'A managed WTO Brexit may give rise to some short-term inconvenience and disruption, but the much greater risks arise from being locked into a very bad deal.'
Mr Johnson repeated the message in his column in the Daily Telegraph today, where he writes: 'This deal is still the worst of both worlds, by which we somehow leave the EU but end up being run by the EU. It is still a complete stinker.'
Warning his fellow MPs about trying to force a second referendum, he adds: 'If they now engage in ludicrous parliamentary jiggery pokery, endlessly tabling amendments designed to frustrate Brexit, they will risk a very serious backlash indeed.
'The answer is not to leave it to Parliament; the answer is for the executive to do its job, as some of us have been advising for months: to accept that the deal is dead, and to move on.'