Dominic Cummings's role in government no longer looks sustainable, as members of the cabinet and Tory MPs turn against him - and in the words of one very senior member of the government, it is "only a matter of time" until the prime minister asks him to go.

The problem for Cummings - and the prime minister - is summed up in a Tweet by the former minister Caroline Nokes: "My inbox is rammed with very angry constituents and I do not blame them."

Nokes is typical, according to ministers and MPs. Like all prime ministers, Boris Johnson risks deep harm to his own authority and popularity if he ignores what his party is telling him.

"What is very frustrating," said one minister "is that Cummings is only an adviser, and yet he is being protected in a way that would never happen to a minister. Jenrick [the housing and communities secretary] almost had to resign for doing something much less serious."

Quite how long Cummings survives in his job depends mainly, ministers think, on how many Tory MPs publicly - and privately (through the whips) - call for him to go in the course of today.

And there is a second ticking time bomb, say ministers. They fear a member of the public may file a complaint to Durham police alleging Cummings broke the Health Protection Regulations - which the police would be obliged to investigate.

This is not to presume Cummings's guilt. He is completely clear he did not break the law. But a criminal investigation would be another embarrassment.

The decision on whether Cummings should stay or go is momentous for the PM. Cummings is the lynchpin of everything that happens in his administration, from the path to full Brexit, to the end of austerity, to the panoply of measures to combat the Covid-19 epidemic.

It is not an overstatement to say that removing Cummings would be the equivalent of removing a significant part of the engine of government. Serious re-engineering would be required, of a magnitude that would daunt Johnson.

But for many Tory MPs and ministers, the risk of keeping him is greater, because it is a risk to public health.

There is a widespread perception that the PM's most important aide bent the quarantine and lockdown rules to suit his own circumstances in an unfair way - which would potentially give licence to millions of others to bend life-or-death rules when the epidemic is a real, present and devastating danger.

"We are expecting the police to enforce the rules," said a minister. "But if we are seen to be protecting one of our own, our authority isn't what it should be."

To put all this in a nutshell, to keep Cummings the Prime Minister would have to go the full Donald Trump and marginalise a significant proportion of his own party. Most who know him say that - despite Johnson’s admiration for Trump’s campaigning ability - he won’t do that.

PS There is a last play to keep Cummings in post in face of pressure from Tory MPs for him to go, but Cummings confident he did nothing wrong - which is to ask Cabinet Secretary to investigate, as requested by Labour. My bet is that’s what will happen. With everything else going on, Cabinet Secretary Sedwill would love that, I am sure.