Jeremy Hunt warned MPs of the risk of 'losing Brexit' today if they reject Theresa May's divorce deal a second time on Tuesday.
The Foreign Secretary said if the Commons crushes the deal a second time, Britain could be forced into a permanent customs union with Brussels - meaning no new trade deals.
Mr Hunt's warning came amid claims today Mrs May could resign by the summer as the price for getting support from Brexiteers.
But even that desperate move 'won't work', ex-Brexit secretary David Davis warned today.
Mrs May faces the prospect of near certain defeat on Tuesday night as weeks of negotiations with Brussels have so far produced no substantial concessions.
The PM must concessions sealed by early tomorrow morning for MPs to vote on them on Tuesday amid speculation she could make a pre-dawn visit to Brussels tomorrow.
In a desperate scramble to win votes, Chancellor Philip Hammond is set to promise MPs a £20billion suspending bonanza in Wednesday's spring statement - but only if they pass the deal.
Despite the push from ministers, Brexiteer rebels and the DUP said today the deal was 'unchanged' meaning a repeat of January's historic defeat was 'inevitable'.
With just hours to the vote, EU negotiator Michel Barnier is not even in Brussels today - instead he is in Dublin for the Ireland vs France Six Nations match.
Talks are only happening on a technical, official-led level - making it highly unlikely a major breakthrough can be made in time.
Former Brexit Secretary Dominic Raab - who voted against the deal in January - warned today only a huge 11th hour concession from Brussels had any chance of saving Mrs May.
Mr Hunt told Marr: 'We have an opportunity now to leave on March 29 or shortly thereafter.
'It's very important we grasp that opportunity because there is wind in the sails of people trying to stop Brexit.'
He added: 'If you want to stop Brexit, you only need to do three things - kill this deal, get an extension and then have a second referendum.
'Within three weeks those people could have two of those three things.
'Quite possibly the third one could be on the way through the Labour Party.
'So we are in very perilous waters.'
Amid a scramble to win the vote, one ally of the Prime Minister told the Mail on Sunday: 'If she has to make that sacrifice in order to secure her legacy, then I think she would.'
Another powerful Downing Street figure added: 'The only way she would countenance going voluntarily is if it could get her deal over the line.'
But Mr Davis told the BBC's Andrew Marr today the plan 'won't get the vote through' because 'this deal is worse than current membership'.
He warned refusing to deliver on the Brexit vote would undermine democracy and predicted it would mean 'Britain will get its Trump moment'.
Mr Davis said MPs will have to choose this week between 'short term but manageable economic turbulence' of a no-deal Brexit or the 'democratic disaster' of no Brexit.
As the Government tries to win the vote Mr Hammond is due to make his Spring Statement on Wednesday afternoon - the day after MPs vote on the deal and hours before they vote on no deal if Mrs May has been defeated again.
He will tell MPs 'serious' money amounting to £20billion is available and a three-year spending review will start in the summer and report in the autumn if the deal passes.
The money will be divided between the public services, targeted tax cuts, long-term investment and keeping Britain's debt burden on a downward trajectory.
A source told the Sunday Times: 'We will be in a position to spend quite a lot of money this autumn.
'Austerity will be well and truly over. But there's no way we can do that until Brexit is resolved.
'We absolutely must have a deal or all bets are off.'
If MPs reject the deal, Mr Hammond will instead axe a three-year spending review and switch the Treasury to a one-year emergency scramble to shore up the economy.
Despite the promises, leading Brexit backers today warn the PM she will lose the vote on Tuesday.
Former Brexit Secretary Mr Raab told Sky News' Sophy Ridge on Sunday the deal was 'near the end of the road' and said the EU had to finally make concessions to save the plan.
He said: 'What we need is legally binding changes, that is what Parliament wants.
'This is for the EU to decide now.'
Tory Steve Baker and DUP Westminster leader Nigel Dodds wrote in the Sunday Telegraph today another defeat as 'inevitable' and Britain should now leave on time with no deal.
The pair want Mrs May to pursue the second part of their so-called 'Malthouse Compromise' that says Britain should ask the EU for a three-year transition period on current terms in exchange for billions of pounds but axe the rest of the deal.
They said: 'It is inevitable that this unchanged Withdrawal Agreement will be voted down again.
'The union of the UK is too precious to put at risk and Eurosceptics do not trust the EU to regulate our economy in the backstop.
'If the Government and parliamentarians want to avoid overthrowing the referendum result and threatening faith in democracy, if they want to avoid the political chaos of a purposeless extension, it is time for them to embrace Malthouse compromise Plan B and leave on March 29, offering all sides the three safety nets of our basic transition agreement.'
The leading candidates to succeed Mrs May –- Foreign Secretary Jeremy Hunt, his predecessor Boris Johnson and Home Secretary Sajid Javid – are all ready to launch immediate leadership bids.
Other potential candidates – including Environment Secretary Michael Gove and Chief Secretary to the Treasury Liz Truss, who are on a joint trip to America this weekend – are 'considering their options'.
Tense negotiations between the UK and the EU are expected to continue all weekend and until late tomorrow, with Ministers in London being updated on the progress by video-link.
Last night, a Downing Street source hinted that a dramatic breakthrough might still be possible by saying that RAF Northolt had put the PM's plane on standby for a last-minute dash to Brussels.
The source said the Prime Minister was 'intensely focused' on making progress but 'these are tough talks we are expecting to go right down to the wire'.
Nerves are still jangling in No 10 following the provocative offer on Friday by the EU's chief negotiator Michel Barnier of limiting the backstop – staying aligned to EU rules – to Northern Ireland only.
No 10 reminded Mr Barnier, who is today planning to be in Dublin for the France-Ireland Six Nations rugby clash, that the idea was first rejected a year ago because it would divide the UK.
On Friday, talks between EU and UK officials continued into the night. Mrs May was briefed in the early hours of yesterday on the limited progress.
Government sources said the current expectation was that Brussels would unveil a 'small concession' on the backstop – but not, they feared, one which would be sufficient to win over all the rebels.
Attorney General Geoffrey Cox, who is leading the efforts to alter the withdrawal agreement, tells today's Mail on Sunday that he will 'not put his name' to any legal opinion which backs the EU's proposals if there is any risk of us being indefinitely detained in the backstop.
'My professional reputation is far more important to me than my reputation as a politician,' Mr Cox says.
The eminent QC reveals that he has been working on an arbitration mechanism which would 'give us the unilateral right to trigger the process that would lead to our exit from the backstop' and would dramatically alter the balance of power between UK and EU negotiators by putting 'the onus on them to prove we can't leave'.
Mr Cox adds: 'It's the reason why some EU officials don't like it – it works.'
Tory whips have warned that the Government could lose the vote by a margin of between 50 and 150 if Mr Cox is unable to change his legal advice – seen as key to winning over Brexit hardliners and the DUP. One senior Cabinet Minister told The Mail on Sunday that Mrs May 'does not have a hope in hell' of winning the vote on Tuesday, with the expectation that 'all hell would break loose' after that.
Defeat on Tuesday would trigger a day of parliamentary drama on Wednesday, with MPs voting on whether to veto 'No Deal' and extend Article 50 – and even the possibility of another no confidence vote in the Prime Minister from Labour.
Downing Street is divided about whether to order Ministers to vote in favour of No Deal – which would risk mass resignations – or put down a motion which only rules out leaving the EU without a deal in March, not at some other point later in the year.
In the wake of a defeat, Mrs May's allies expect pro-Remain MPs, led by Labour's Yvette Cooper, to seize control of the process to both delay Brexit and 'soften' it by keeping the UK in a customs union.
They have been urging Tory MPs to 'save Brexit' by voting for the deal for fear of much worse.
But last night, Tory Brexiteer leader Jacob Rees-Mogg – chairman of the party's European Research Group – denied that voting down the deal would hand control of the process to a Remain-dominated Commons. He told The Mail on Sunday: 'Brexit can only be blocked if the Government wants to do it. That would be a breach of all its commitments.
'If the Government holds steady, Parliament cannot stop Brexit.'
The approach of the crunch vote has led to tensions spilling over in Cabinet meetings.
Last week, Home Secretary Sajid Javid clashed with Philip Hammond over the Chancellor's plans to bail out the economy if the UK leaves the EU without a deal.
The Chancellor – who has been widely criticised within Government for failing to devote signifi-cant funds to No Deal planning – was rebuked by the Home Secretary for belatedly setting up a fund to jump-start the economy if talks with Brussels collapse.
Mr Javid told Mr Hammond at a meeting of Theresa May's Brexit 'doomsday committee' last week that he didn't think that he or his Treasury officials were 'properly equipped' to make such 'commercial judgments'.
The 21-member EU exit and trade (preparedness) committee was established by Theresa May 'to streamline the process to oversee the delivery of plans for an orderly exit from the EU'.
It has been dubbed the 'doomsday' committee because it is obliged to countenance the worst-case scenarios of a No Deal Brexit.
The committee was discussing Project Kingfisher, which The Mail on Sunday revealed last month was the codename for Mr Hammond's secret bailout fund. It includes the establishment of a short-term fiscal stimulus package designed to prop up the UK's manufacturing and industrial sectors, with Ministers ordered to draw up top-secret lists of specific firms and sectors they believe will most need the money.
Mr Javid is also overseeing his own No Deal disaster committee codenamed Operation Snow Bunting, designed to deal with civil unrest and rioting in the wake of a messy EU divorce.
Chancellor Philip Hammond will use his spring statement this week to pledge a £200 million, post-Brexit push to keep Britain as a scientific world leader – including the creation of a national super-computer in Edinburgh to aid medical, climate science and aerospace research.
This article has been adapted from its original source.
© Associated Newspapers Ltd.