A defiant Boris Johnson has made it made it clear he is not giving up his grip on power, despite calls from ministers and MPs across the Tory Party to stand down.
No prime minister in modern history has tried to cling on to office in the face of such overwhelming opposition from their own side.
It places the ball firmly in the court of those who believe his position has become untenable.
– What can be done to remove Mr Johnson from No 10?
In the first instance, the focus will fall on the Cabinet.
So far most of Mr Johnson’s top team remain in their positions, despite Home Secretary Priti Patel and newly-appointed Chancellor Nadhim Zahawi being among those calling on him to go.
Mass resignations by the Cabinet – accompanied by more quitting in the lower echelons – could be enough to force his hand if it leaves him unable to form a functioning government.
However there are no guarantees this will happen, particularly if the Prime Minister is determined to carry on with a depleted administration.
– What else is there?
Next it goes back to Conservative MPs if they want to make a fresh push to oust him.
Traditionally it would be up to Sir Graham Brady, the chairman of the backbench 1922 Committee, to go to the Prime Minister and tell him he has lost the support of his MPs and should go.
If that fails, on Monday elections are being held to the 1922 executive which is responsible for setting the leadership rules.
Currently Mr Johnson is safe from another vote of confidence for 12 months after surviving a challenge last month.
However, if he is still in place, the new executive is likely to consider a rule change which could allow a second confidence vote – possibly before MPs break for the summer later this month.
– If he lost such a vote would Mr Johnson have to go then?
That would mean he was out as party leader – but not necessarily as Prime Minister.
Reports have suggested he could refuse to quit a premier, but instead seek to call a snap general election – citing his mandate from 14 million voters in the last general election.
That would clearly be a nuclear option, raising a huge number of practical issues.
Some senior Tories believe senior civil servants would seek to deter him, warning it would be “inappropriate” to put the Queen in a “difficult position” by asking for a dissolution in such circumstances. But would he listen?
– So what is the end game?
Under the UK’s unwritten constitution, any prime minister derives their authority from their ability to get their government’s business through Parliament.
If the Government loses a major piece of legislation – particularly a money bill – then the Prime Minister would be expected to go.
Alternatively, Tory MPs could combine with the Opposition to defeat him in a vote of confidence by the House of Commons – something they would normally be deeply reluctant to do.
And if all of that fails, the country really will be entering uncharted waters.