The Liberal Democrats and a “significant number” of Tories would support a no-confidence motion in the Government, according to former business secretary Sir Vince Cable.
The ex-leader of the Liberal Democrats said the UK has been in a constitutional crisis “for quite a long time”.
Speaking on BBC’s Newsnight, Sir Vince said there would be wide support for an “emergency administration” to take over if Prime Minister Boris Johnson loses a motion of no confidence.
Asked whether the UK is facing a constitutional crisis, Sir Vince said: “I think we are already in one. We have been in one for quite a long time.”
He added: “The extreme no-deal Brexit can be stopped. I think we need to look at it partly from a political question point of view.”
Sir Vince said some MPs would not be able to support a new Government led by Jeremy Corbyn, but that they may be able to support a “more broadly based group”.
He said Parliament would reject a no-deal Brexit because the “consequences are so dire”.
He said when no-deal is “staring MPs in the face” many would “get behind” an emergency administration.
Sir Vince added: “We would certainly support a no confidence motion, and I think a significant number of Tories would do as well. And that is the way we are going to stop this.”
As it stands, under the latest extension to the Article 50 withdrawal process by the EU, Britain is due to leave on October 31.
If Mr Johnson is defeated in a no-confidence motion he would have 14 days, under the Fixed Term Parliaments Act, to win another vote of confidence or, if no other government could be formed, face a general election.