Boris Johnson used one of his final speeches in the Commons to suggest Sir Keir Starmer was plotting with the “deep state” take Britain back into the EU.

The prime minister used the phrase beloved by paranoid conspiracy theorists, as he repeatedly claimed the Labour leader wanted to undo Brexit.

“We got Brexit done, and the rejoiners and revengers were left plotting and planning and biding their time,” Mr Johnson said, before suggesting his legacy was under threat.

He said: “Some people will say as I leave office that this is the end of Brexit … and the leader of the opposition and the deep state will prevail in its plot to haul us back into alignment with the EU as a prelude to our eventual return.”

Challenging Tory MPs to uphold his hard Brexit deal, Mr Johnson added: “We on this side of the House will prove them wrong, won’t we?”

Last month Sir Keir vowed not to take the UK back into the EU single market or customs union, or restore freedom of movement, as he set out his plan to “make Brexit work”.

Mr Johnson pointed to Starmer’s record voting against Brexit deals, claiming he had tried to “overturn the will of the people” – and would attempt to overturn Brexit again if he became PM.

The outgoing PM said: “Be in no doubt, if he were ever to come to power with his hopeless coalition of Liberal Democrats and Scottish nationalists, he would try to do so again at the drop of a hat.”

Sir Keir fired back by accusing Mr Johnson of indulging in sheer fantasy when it came to his legacy. “The delusion is never-ending – what a relief for the country that they finally got round to sacking him,” he said.

The Labour leader added: “He’s been forced out in disgrace, judged by his colleagues and peers to be unworthy of his position and unfit for office.”

Mr Johnson won cheers from Tory MPs when boasting of his party’s 2019 election victory over Labour, claiming they had “sent the great blue ferret so far up their left trouser leg they couldn’t move”.

He also added he believes Tory MPs will prove Sir Keir “totally wrong” over the prospect of a Labour election triumph, adding they will send the opposition leader “into orbit”.

MPs will stage a vote of confidence in the government on Monday evening at around 10pm, amid renewed calls from the opposition for Mr Johnson to step down immediately and hand over to a caretaker.

Labour former minister Dame Margaret Hodge said: “This debate is essential to call a halt to the dangerous Trumpian assault on everything we value in our British democracy.”

But Tory MP Sir Edward Leigh said he “wholly regrets the departure of this prime minister and I remain completely loyal to him to the very end ... And I think we will ask ourselves, what have we done?”

“Where is any sense of kindness? Or magnanimity? Why do we need to throw these insults around?” he added about Sir Keir’s condemnation. The loyalist said it was not as if Mr Johnson was “the worst sort of mass murderer and criminal in political history”.