Boris Johnson could be leading Britain into its biggest constitutional crisis since the civil war, a Tory grandee has warned.

Sir Malcolm Rifkind, an ex-foreign secretary, urged the new prime minister to reject the advice of his advisers and not follow the lead of King Charles I by making a "mockery" of parliament.

He told Sky News Mr Johnson should not copy the former monarch's example or else risk "losing his head".

Image: Charles I was executed after the English Civil War

Sir Malcolm instead urged the prime minister to "follow the advice of Churchill", who once said politicians shouldn't kill themselves "because they might live to regret it".

The row centres on Britain's increasing chance of leaving the EU with no deal on 31 October.


Mr Johnson has promised Brexit "do or die" in less than 90 days, but faces the threat of a no-confidence vote fuelled by fears over no-deal and his refusal to rule out suspending parliament to force it through.

But his most senior adviser has reportedly told MPs it is too late to stop Britain leaving the EU without a withdrawal agreement on Halloween.

According to the Sunday Telegraph, Dominic Cummings said even if the move to oust the prime minister was successful, he could simply call an election after Brexit had happened automatically.

In such circumstances, MPs would have 14 days to try to form a new government, with the Queen potentially put in an unprecedented position where she could face calls to intervene to remove Mr Johnson if he refuses to resign.

Sir Malcolm said a no-deal Brexit was an "entirely respectable objective" but that Mr Johnson had to get consent for it, either from MPs in parliament or the public through an election or referendum.

He told Sky News: "What you cannot have is be forced into a general election with the election deliberately, not necessarily but deliberately, dated after we have already left the EU.

"That makes a mockery of the electorate having the last word as to what affects the future of this country."

Image: Britain is due to leave the EU on 31 October

Sir Malcolm added: "The last person who tried what is being suggested was King Charles I.

"That led not only to the English Civil War, but it led to him losing his head.

"I don't believe Mr Johnson wishes to put himself in comparable position."

Labour MP Peter Kyle, who is a leading figure in the campaign for another referendum, said if Downing Street broke the rules, parliament would make new ones.

"Government cannot step outside convention and expect the Commons to remain bound by it. Charles I found this out the hard way," he warned.

Sir Malcolm had also urged the prime minister to "slap down" his most senior adviser, Dominic Cummings, "and his ilk" for trying to force through no-deal.

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Earlier, Mr Cummings insisted preparations for the scenario were going "great" but hit back at criticism from Tory MP Dominic Grieve, who accused him of "characteristic arrogance and ignorance" about the British constitution.

In his first public comments since joining Number 10, Mr Cummings told Sky News on his way to work on Wednesday: "I don't think I am arrogant. I don't know very much about very much.

"Mr Grieve will see what he's right about."