Brexit has been dealt a hammer blow after Theresa May’s plans fell to the biggest ever Commons defeat and Jeremy Corbyn launched a bid to topple her government within 24 hours.

Even Downing Street insiders admitted being shocked by the scale of the rout, which sent shockwaves across the English Channel and saw critics brand her deal “dead”.

In total, 118 of the prime minister’s own MPs refused to back the withdrawal agreement she spent 19 arduous months negotiating with Brussels.

Labour leader Mr Corbyn branded the result “catastrophic” and immediately said he would table a motion of no confidence, which Ms May must win on Wednesday to avoid a general election.

The prime minister will simultaneously begin a desperate scramble to save her deal, meeting senior parliamentarians from across the political spectrum to see what changes she might seek to win support.

But sources from both the pro-EU and Eurosceptic wings of the cabinet admitted to The Independent in the aftermath, that a softer Brexit was now a more likely outcome.

Ms May’s spinners had briefed that they hoped to limit the number of Tory MPs opposing her to double digits, with many people thinking Conservative opposition would weaken as the big moment approached.

But there were gasps as the result was read out – 432 votes against and just 202 for – making it a bigger margin of defeat than the previous comparable loss suffered by Labour’s Ramsay MacDonald in 1924.

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Even Ms May’s spokesperson was forced to admit it was a “significant result” in a briefing afterwards, justice secretary David Gauke said it was “disappointing” and another senior source said it was “heavier than is comfortable”.

One cabinet insider from the Remain camp told The Independent: “She’s going to be under enormous pressure to back a customs union”.

The result of tonight’s vote is the greatest defeat for a government since the 1920s in this House. This is a catastrophic defeat Labour leader Jeremy Corbyn

Another from the Brexiteer wing admitted: “Where next? It makes a soft Brexit more likely.”

Ms May told the Commons in the wake of the defeat that “this government will listen” to the result, and she announced she would hold cross-party talks with MPs across the house to determine a way forward before going back to Brussels.

Her aides said she would enter these talks with “principles” that any deal should allow the UK to hold an orderly Brexit, leave the country in control of its money, borders and laws and with an independent trade policy.

But spinners shied away from calling these “red lines” suggesting some of the strong positions set out by Ms May up to now may be moveable.

Michel Barnier reacts to parliament's rejection of Theresa May's Brexit deal: 'Now it's time for the UK to tell us the next steps'

A key facet of Mr Corbyn’s approach is a customs union with the EU, but this could kill off the chances of the UK implementing an independent trade policy from Brussels, and would also risk badly splitting her own party.

As he announced he would table a confidence vote in the government, Mr Corbyn said in the Commons: “The result of tonight’s vote is the greatest defeat for a government since the 1920s in this House. This is a catastrophic defeat.”

But after the DUP and Brexiteer rebels said they would back Ms May in the confidence vote, she looked set to overcome that initial hurdle – leading to questions over what Mr Corbyn would do next.

Labour MPs set to come out in support for a new referendum looked like they would be disappointed as their leader’s spokesperson indicated Mr Corbyn would first pursue other avenues.

Jeremy Corbyn launches bid to topple Theresa May in aftermath of major Brexit defeat

Ex-education secretary Justine Greening said Ms May’s deal was now “dead” as she restated her belief that the only way forward was a Final Say referendum – something The Independent has campaigned for.

European Council president Donald Tusk also appeared to indicate that the UK should now have a second referendum, while Commission president Jean Claude Juncker said Britain needed to set out its intentions adding “time is almost up”.

Before the vote on her deal Ms May appealed to MPs to understand the magnitude of their decision, telling them: “This is the most significant vote that any of us will ever be part of in our political careers.

“A decision we will have to justify and live with for many years to come. A vote against this deal is a vote for nothing more than uncertainty, division.”

But it was not enough, neither was a push from the prime minister and her attorney general Geoffrey Cox to convince her critics in the final hours before the vote, with many standing in the Commons debate to declare their opposition.

Theresa May gives speech before Brexit meaningful vote

Tory former attorney general Dominic Grieve called Mr Cox’s performance at the despatch box “entertaining”, but said it filled him with “gloom” to see that the government having to “rely on the advocacy skills of a criminal defence advocate”.

Leaping on Sir Geoffrey’s analogy of the withdrawal agreement as an “airlock” leading to a better future, he said: “I’m afraid my own view is that we will either choke to death in the airlock as a nation or when the door finally opens we will find the landscape little to our liking.”

Conservative chair of the defence committee Dr Julian Lewis said: “Because Brexit should mean Brexit and no deal is better than this bad deal, I shall vote no, no and no.”

Much of the opposition to Ms May’s deal focusses on the hated “Irish backstop” which would come into play if no future trade relations with the EU are agreed by December 2020, at which point the UK would find itself in a potential indefinite customs union until a new deal were decided.

John Barron MP and Sir Edward Leigh both tabled amendments that sought to give the UK the unilateral right to leave the backstop, amid fears it could become permanently stuck in it.

Both were rejected by the government however, which claimed they would undermine the withdrawal agreement.

A further agreement which might have mitigated the government’s defeat was not chosen for a vote by the speaker John Bercow, leading to further Tory anger over his continued role in parliamentary proceedings.