Boris Johnson will seek to hold a snap general election in six weeks if he loses a key House of Commons vote today.
The dramatic move comes as a cross-party coalition of MPs, including Tory former ministers such as Philip Hammond, try to seize control of the parliamentary agenda in order to pass a law blocking a no-deal Brexit.
If passed, it would force Mr Johnson to ask the European Union to delay Brexit until January 31 – or any alternative date that Brussels demands.
Tory whips have already warned that any of their MPs who vote against the Government will be suspended from standing again as Conservative candidates.
In a statement on the steps of Downing Street, Mr Johnson said if MPs were successful it would “plainly chop the legs out from under the UK position and make any further negotiation absolutely impossible”.
He added: “To show our friends in Brussels that we are united in our purpose, MPs should vote with the Government against Corbyn’s pointless delay.
“I want everybody to know – there are no circumstances in which I will ask Brussels to delay. We are leaving on October 31, no ifs or buts. We will not accept any attempt to go back on our promises or scrub that referendum.”
A senior UK Government source later reiterated the point, saying: “The prime minister is not going to get into a position where he is sent to Brussels by Parliament to negotiate a deal that Parliament has said could be an extension, which essentially would be about cancelling the referendum.”
He added: “MPs are effectively considering whether to hand control of the negotiations to Jeremy Corbyn.
“That would be shooting ourselves in the foot and, if Conservative MPs help him to make no deal illegal tomorrow and therefore create another pointless delay, the government’s negotiating position will be wrecked.
“What they are effectively voting for is to hold a rapid election. And they will have to explain what they are doing.”
SNP Westminster leader Ian Blackford said MPs should ready themselves for the “parliamentary fight of their lives”.
He said: “We are in unprecedented territory as Boris Johnson’s rogue Tory government continues to ride roughshod over our democracy in an attempt to force through an extreme Brexit, which we know will be devastating for jobs and people’s living standards.
“SNP MPs stand ready for the parliamentary fight of their lives to stop Brexit and to ensure that democracy is not shut down.
“With time running out it’s clear that the threat to Scotland is growing. Economic analysis has already shown that any form of Brexit will be devastating for people in Scotland – with a no-deal exit costing up to 100,000 jobs and hitting people’s pockets to the tune of £2,300 a year per person. That is a price that our constituents must not pay.”
Far North MP Jamie Stone added: “Boris Johnson’s determination to crash out of the EU shows how little he cares about Scotland or my constituents. He has no mandate for a no deal Brexit which will be catastrophic for the country.
“The prime minister’s empty words show nothing has changed and we must stop this undemocratic power grab.”