Jo Swinson urges Jeremy Corbyn to back no-confidence motion in Boris Johnson

Ms Swinson has written to Jeremy Corbyn, who, as leader of the opposition, is the only person who can trigger such a parliamentary showdown, calling for him to move against the Government.

Referring to Mr Corbyn, the Lib Dem leader said: "It is time he stops aiding and abetting this Conservative Brexit and act."

The letter to the Labour leader, which has cross-party support, states: "Boris Johnson does not hold a mandate from Parliament or the general public to be Prime Minister.

"His reckless refusal to rule out proroguing Parliament in order to crash the UK out of the EU without a deal demonstrates that he is not fit to lead this country.

"As the Leader of the Official Opposition you are the only person in the position to call a vote of no confidence in the new Prime Minister.

"We therefore urge you to do so immediately.

"You must not sit back and allow this government to crash our country out of the EU.

"We implore you to take action and call for a vote of no confidence.

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"It is vital that we work together to secure a people's vote with the option to stay in the EU."

Ms Swinson has also tabled an Early Day Motion (EDM) expressing no confidence in Mr Johnson.

It states: "This House has no confidence in the Prime Minster; rejects the option of the UK crashing out of the EU; and rejects the option of Parliament being prorogued before Friday November 8 2019."

However, EDMs are traditionally used as a parliamentary device to highlight issues and are not voted on by MPs.

Labour has said that a no-confidence vote is a "nuclear option" and they want to ensure it would pass with the support of rebel Tories before triggering such a move.