The national security of the UK is under threat as a result of the mass resignations from Boris Johnson’s Government, a constitutional law expert has claimed.

Professor Adam Tomkins, a former Scottish Conservative MSP, said the scale of the exodus – which began with Sajid Javid and Rishi Sunak on Tuesday – now means a “constitutional crisis is beginning to unfold”.

With the latest resignations including security minister Damian Hinds and Northern Ireland Secretary Brandon Lewis, Prof Tomkins warned: “It is no exaggeration to say the national security of the United Kingdom is at threat.”

He said it is now a “constitutional imperative” for Mr Johnson to go, calling on the 1992 Committee of Tory backbenchers to accelerate its plans to change its rules to enable another vote of confidence in the Prime Minister.

Prof Tomkins told BBC Radio Scotland’s Good Morning Scotland programme: “My view is the 1922 Committee needs to accelerate its plan. It’s plan clearly was there would be elections to the executive on Monday, that executive would be formed of people who want to change the rules to enable a second vote of confidence in Boris as leader as early as Tuesday of next week.

“It now looks like that is too late because we need to have functioning government over the weekend, we need to have a functioning government now.

“We don’t have a functioning government now because there is straightforwardly an insufficient number of Conservative MPs who are willing to serve in a Government headed by Boris Johnson.”

He said Mr Johnson “is not an honourable man” and is “clinging to power in what is increasingly becoming an unconstitutional manner”.

Prof Tomkins said: “What we have in the United Kingdom is a Government which is so skeletal and so missing of key personnel that it is no exaggeration to say the national security of the United Kingdom is at threat.

“We have no security minister, Damian Hinds resigned a few minutes ago. We have no Secretary of State for Northern Ireland, Brandon Lewis resigned an hour or so ago.

“These are key roles which have to be fulfilled by ministerial appointment in order to maintain the security of the United Kingdom.

“So what we have at the moment is a Prime Minister who is unable to form a government, or appears unable to form a government.”