On Friday, Sajid Javid, the Health Secrteary, said Sir Keir had done a “good job” when he was Director of Public Prosecutions, adding: “He should be respected for it – it is a tough job, and he deserved absolute respect for that. But the Prime Minister has also come out and clarified those remarks, and that is important.”

However, critics of Mr Johnson in his own party called on the Cabinet to act now.

Andrew Bridgen, the MP for North West Leicestershire, said: “It’s now down to the Cabinet. Leaders walk towards problems and solve them and confront them – they don’t run away from them.”

Mr Bridgen said the Tories had “a big problem”, adding: “In the leadership election which will surely ensue, I hope they don’t come and try and canvass me for support if they don’t show the leadership we require now. The country and the party require them to act as leaders.”

Three Conservative backbenchers who have been critical of Mr Johnson have said the “complete shambles” in Downing Street will lead to more letters of no confidence being submitted to Sir Graham Brady, the chairman of the 1922 committee.

They said a spin operation from Mr Johnson’s loyalists would not convince wavering Tory MPs that the resignations were planned.

“This idea that the PM is showing strength when people quit is just daft,” said one senior MP. “He’s had a clearout and now there’s nobody in the building – it’s just bizarre. We will see more attrition. This is on a set course of letters of no confidence – we just don’t know the speed.”

PM’s close circle now ‘a field of short poppies’

Another former minister told The Telegraph: “There probably is a growing sense of inevitability about all of this, which may have moved the dial.

“I don’t think it shows he is in control. He didn’t want her [Munira Mirza] to leave – that’s not in his control. If you were going to do something that is a planned action, you’d have the replacements ready.”

The former minister said Mr Johnson’s close circle was now “a field of short poppies”.

A government source said that while the resignations “could be a cleaning out the Augean stables moment, if more people like Munira and Elena [Narozanski] go, it’s a collapse”.

A third MP said: “The reason people put in a letter of no confidence in the Prime Minister is because they’ve got no confidence in the Prime Minister, not in his principal private secretary. That’s what it ultimately boils down to.

“I think more will put them in because they just think the whole thing appears chaotic, and so it sort of moves on from people’s original reasons for being disgruntled. So then it’s just the sense that it’s a complete shambles.”