Mr Corbyn made clear the party is on high alert to try to force the PM out and a general election.
He suggested the Brexit date will have to be delayed if he succeeds, but repeatedly refused to be drawn on whether Labour would campaign on a manifesto to take the UK out of the EU.
He also declined to say if he would back a second referendum, as is being demanded by dozens of his own MPs.
Asked in an interview on the BBC’s Andrew Marr show whether a no-confidence vote would happen immediately if, as expected, Mrs May’s package is rejected by the Commons on Tuesday, Mr Corbyn replied: ‘It is going to be soon, don’t worry about that.’
Despite desperate last-ditch pleas, Mrs May is still facing a massive defeat in the crunch Brexit vote with hardline Remainers and Brexiteers mobilising in a bid to thwart her plans.
Pro-EU rebels are said to be plotting a ‘coup’ against the government afterwards to give Parliament control of the negotiations with the EU and rule out a no-deal departure.
On the BBC’s Andrew Marr show today, Jeremy Corbyn made clear the party is on high alert to try to force the PM out and a general election
Theresa May (pictured at church in her Maidenhead constituency today) is facing a disastrous defeat on her Brexit deal this week
Mr Corbyn has so far resisted pressure from his own ranks to force a confidence vote, with allies insisting there is no point as the government would win.
But there have been mounting signs that he is ready to take advantage of Mrs May’s moment of maximum weakness.
In the interview today, Mr Corbyn said: ‘The crucial thing is Tuesday. And then, if this Government can’t control Parliament, it’s time to have a general election.’
Ducking and diving as he was pressed on whether Labour would campaign on a manifesto to deliver Brexit, Mr Corbyn said ‘we’re campaigning for a country that is brought together by investment’.
He added later: ‘We’re campaigning for a customs union.’
The Labour leader said his party will ‘decide our manifesto content as soon as we know there’s an election coming’.
Pressed about the option of a second referendum, Mr Corbyn stressed his preference for a general election.
He added: ‘My own view is that I’d rather get a negotiated deal now, if we can, to stop the danger of a no-deal exit from the EU on March 29 – which would be catastrophic for industry, catastrophic for trade and the long-term effects of that would be huge.’
Asked if Article 50 needed to be extended, Mr Corbyn said: ‘Clearly if Theresa May’s deal is voted down, clearly if a general election takes place and a Labour government comes in – an election would take place February, March time – clearly there’s only a few weeks between that and the leave date, there would have to be time for those negotiations.’
He also defended Common Speaker John Bercow over accusations he has been conspiring with Remainer MPs to frustrate the Brexit process.
‘I think he is a very good Speaker,’ Mr Corbyn said.
Earlier today, Shadow business secretary Rebecca Long-Bailey said the odds of Labour tabling a vote of no confidence in the Government would ‘increase dramatically’ if the Prime Minister’s Brexit deal falls.
She told Sky News’s Sophy Ridge On Sunday: ‘Ultimately the decision rests with Jeremy (Corbyn) and it’s up to him to determine when we do put forward that vote of no confidence, but it’s certainly a case of when, not if.’
Mr Corbyn defended Common Speaker John Bercow (pictured) over accusations he has been conspiring with Remainer MPs to frustrate the Brexit process
But Labour MP John Mann underlined the splits Mr Corbyn faces in his own party, confirming he will vote for Mrs May’s deal.
Mr Mann said he expected some of his colleagues to support it too, but added: ‘I’d be surprised if it’s anything like enough to get this deal through, but things could change.’
Labour has revealed Mr Corbyn will unveil a new party political broadcast on Wednesday.
The party also announced that it was hiring pollsters for the next Election ‘to test policies and the impact of campaigning in key marginals’ and had selected 100 candidates for the closest-fought seats.
Labour sources claimed that the most recent polling showed that the country has ‘moved economically to the Left’.
One said: ‘While the Government has been locked in bitter infighting and chaos over their botched Brexit negotiations, the needs of the country have been neglected. Tory austerity has left the majority of people worse off, creating a cost of living crisis and levels of poverty not seen since the 1930s.
‘Our Election campaign strategy will set out a positive vision of how we will make the country better, one of fairness and good public services, where we support each other.’
Brussels last-ditch mission to save deal
Brussels’ most senior Eurocrats are set to publish two letters tomorrow in a last-ditch effort to help Theresa May get her Brexit deal through the Commons.
The Mail on Sunday understands EU Commission president Jean-Claude Juncker and EU Council president Donald Tusk will each send a separate letter designed to reassure MPs over the controversial ‘backstop’ measure that could see the UK locked to EU rules indefinitely.
But the correspondence is likely to fall far short of the demands of Tory Brexit rebels who want the Prime Minister to reopen talks with the EU to rip out the fallback from the terms of her withdrawal agreement.
EU Commission president Jean-Claude Juncker and EU Council president Donald Tusk will each send a separate letter designed to reassure MPs over the controversial ‘backstop’
Brussels sources say that Mr Juncker’s letter will vow to ‘expedite’ trade talks between the EU and the UK to try to avoid the ‘backstop’ ever being triggered.
He will set out a process for a new trade deal to be done as quickly as possible but is unlikely to include a date for talks to start.
Meanwhile, Mr Tusk will reiterate the 27 other EU countries have a ‘firm determination’ to have a new relationship with Britain in place by the end of 2020 to avoid the measure kicking in.
He will add that if the deal is not ready by that point, all European states will work to have it signed by 2021 at the latest, meaning the UK would only have to shadow EU trade and customs rules for an additional year.
Last night Downing Street insiders said they expected the letters to be published on Monday evening for maximum impact ahead of Tuesday’s Commons showdown.
Even with a trickle of Tory MPs climbing down from their opposition to Mrs May’s deal, she is on course for an defeat of historic proportions. After three full days of debate, Mrs May’s allies are braced for a thumping defeat, with efforts focused on keeping the tally to ‘under three figures’.
Mrs May will likely address MPs and the public late on Tuesday evening or early on Wednesday, with Ministers expecting her to announce yet another trip to Brussels to try to squeeze more concessions from the EU.
Officials in Brussels, Dublin and London are all said to be ‘acutely aware’ that the backstop is the last major sticking point to a deal being done, with the Irish government expected to come under increased pressure to soften their objections to the measure being watered down.
But last night Brussels sources said in response to the likely defeat, attention would instead begin by focusing on a rewriting of the non-legally binding political declaration that sets out EU and UK hopes for future trade arrangements rather than reopening the withdrawal agreement treaty on the terms of divorce.