Labour could try to bring down the Government in an effort to block a no-deal Brexit, Sir Keir Starmer has said.
The Shadow Brexit Secretary told the Parliamentary Labour Party he is prepared to work with MPs from across the Commons to prevent the UK crashing out of the European Union without a deal.
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Labour would be prepared to use any parliamentary measures at its disposal, including tabling a motion of no confidence in Theresa May's Government.
If such a motion passed, a new government would have to be formed within 14 days and win a confidence vote in the House of Commons.
If the new administration could not do so then there would be a general election.
'Miserable failure of negotiation'
Sir Keir was expected to tell the meeting of the PLP on Monday: "The deal the Prime Minister has brought back is a miserable failure of negotiation. It falls far short of a deal Labour could support.
"If Theresa May's deal fails to command the support of Parliament, then we will not stand back and allow her to take this country off a cliff.
"No deal is not an option. Labour will not countenance no deal - and nor would many of the Prime Minister's own MPs.
"It would be politically unsustainable for any government to deliver a no deal without the consent of Parliament.
"There will be opportunities to make the majority against no deal heard. Motions will be tabled, amendments will be pressed and a no-confidence vote can be triggered.
"And let me be clear: Labour will work with all sides to make that happen."
The Opposition could use the passage of legislation required in advance of Brexit to table amendments aimed at ruling out a no-deal departure.
Labour could also use the time it is allocated for opposition day debates to attempt to win support for its position.