Supreme Court rules that MPs are in charge and Boris Johnson is their servant, writes Robert Peston

There is no precedent for the Supreme Court finding that a PM acted unlawfully when advising the serving monarch.

There is no precedent for the Supreme Court ruling that an order in the Privy Council to prorogue parliament is nul and void.

There is no precedent at all for the August and Magisterial ceremony in parliament that sends MPs and Lords home being ruled by judges as a pointless exercise that should now be viewed as never having taken place.

There is no precedent for judges to have ruled that parliament is in effect still sitting, that legislation that had been thought to have been lost is in effect still alive, after MPs and Lords had been told by the PM that there services were not required for five weeks.

Johnson's single biggest act since becoming PM in July, sending locking MPs and Lords out of their debating chambers, has been ruled as a grotesque breach of the UK's unwritten constitution.

The PM has been humbled in the courts like no PM in history.

So what on earth happens now?

The PM has been humbled in the courts like no PM in history. Credit: PA

The most important point is that the Supreme Court has formalised that Boris Johnson's minority government is the servant of the House of Commons, and it will intervene to prevent any attempt by him to neuter MPs' power.

That means he is their captive. That when they say "no to no-deal", he has no route left to get round them.

So he has a choice. He can work with MPs to find a compromise. Or he can quit.

Ian Blackford, Gina Miller and Joanna Cherry looked elated at the Supreme Court ruling. Credit: PA

Now you might think the PM would resign, given that the extent of today's humiliation and that his aim of Brexit by October 31, deal or no-deal, "do or die," now looks wholly undermined, impossible.

Boris Johnson said last night there was no chance of him quitting.

What we don't know is whether he will abandon his ruthless single track route to Brexit on October 31 and try to govern in a more consensual way.

If he fails to do that, MPs could hold a vote of no confidence in him and install a caretaker prime minister.

But enough MPs have said they can't support Jeremy Corbyn as caretaker, so that option is probably still closed - unless and until the Lib Dems and rebel Tories drop their opposition to Corbyn becoming temporary PM, which I don't expect.

Could Jeremy Corbyn step aside to make way for a caretaker PM? Credit: PA

Could Corbyn swallow his pride and allow a less divisive MP - a Margaret Beckett or Ken Clarke - to become a temporary PM, head of a government of national unity?

Maybe. But it is dawning on those who originally promoted the idea of a caretaker PM to sort Brexit that doing so is fraught with difficulties - not least of which is that upwards of 100 MPs from all parties would have to be found to fill vital ministerial posts, and it is not clear how that could be done in the absence of parties uniting in a formal coalition.

It is an awful mess.

It is not even clear when MPs will convene again or whether the Conservative Party Conference can go ahead in these fraught conditions.

There is only one certainty.

MPs are in charge; Boris Johnson takes orders from them.