Katya Adler
Europe Editor

Privately EU contacts have described the ruling to me as humiliating and an embarrassment for Boris Johnson.

But on the ground, when it comes to negotiations, the ruling changes very little.

It’s seen by the EU as a domestic political matter. The EU is not a player in that so it prefers to concentrate on where it actually has a role to play – and that is in negotiations.

After three years of Brexit debate, EU leaders would be delighted to have a deal signed, sealed and delivered by mid-October, as Boris Johnson wants, but they’re extremely sceptical about that.

And of course, the Supreme Court ruling does not change that at all.

Foreign Secretary Dominic Raab is to leave the United Nations General Assembly early ahead of Parliament resuming tomorrow.

A Foreign Office spokesperson said: “The foreign secretary will be returning to the UK this evening to be in Parliament tomorrow, where he plans to update MPs on the situation with Iran."

Image source, Getty Images

German Chancellor Angela Merkel says the significance of the Supreme Court decision is "a domestic debate for Britain to have".

Speaking at the UN summit in New York, she added: "I continue to hope that we achieve a deal - as it is being called - or a treaty for the orderly exit of Britain from the EU.

"We are prepared for the other option but would prefer an orderly Brexit treaty."

Brexit Party MEP Belinda de Lucy says she has the utmost respect for the UK courts but she believes it is “dangerous territory” when the judiciary “step into the sphere of politics”.

“We believe the sovereignty lies with the people,“ she said.

She also refuted suggestions that the Brexit Party might scupper Brexit, saying that in the event of a general election her party had offered to stand down candidates in areas where there were MPs who supported a “clean Brexit”.

“We’ve offered it to Boris. He’s rejected it so far so really the ball lies in his court. If he want to split the Brexit vote… then the blame rather lies with him.”

BBC One

Labour MP Dan Carden says Boris Johnson should seek an extension to Brexit to enable a general election.

He said Labour wouldn't support a vote of no confidence now because of the threat of crashing out of the EU without a deal.

“We have to take the risk of crashing out of the European Union off the table. Boris Johnson is playing games,” he said.

He called Mr Johnson "a duplicitous" prime minister and said he would like to see a vote of no confidence in him but "it has to be moved at the right time".

Canadian Prime Minister Justin Trudeau said the UK's focus on Brexit is undermining the country's needed leadership in global affairs.

Asked to comment on the UK Supreme Court ruling, he said: "We've seen the instability and the challenges that the UK continues to go through as it is wrapped up with this issue."

"But we certainly deplore that they are so consumed by this issue that it is interfering with their ability to lead on so many other things where the UK's leadership in the world is so necessary."

A spokesperson for the attorney general's office - the government's chief legal adviser - says the government "acted in good faith and in the belief that its approach was both lawful and constitutional".

"These are complex matters on which senior and distinguished lawyers have disagreed," the statement says.

"The Divisional Court led by the Lord Chief Justice agreed unanimously with the government’s legal position, as did the Outer House in Scotland.

"We are disappointed that in the end the Supreme Court took a different view. We respect the judgement of the Supreme Court."

Irish Prime Minister Leo Varadkar has been holding talks with Boris Johnson in New York.

Mr Varadkar says they had a good meeting but had not reached an agreement on how to resolve their differences over Brexit, adding "we got into some more details".

"We are very keen that there be a deal, that the UK should be able to leave the European Union in an orderly fashion," he said. "That's in Ireland's interest - it's in Britain's interest too."

Image source, Getty Images

DUP deputy leader Nigel Dodds says while the ruling "has taken most constitutional experts by surprise", the government must respect and abide by the judgement.

However, he says ultimately it means it is less likely the UK will leave the EU with a deal.

"All of these shenanigans in Parliament, all of these manoeuvrings by parties to shackle Boris Johnson's hand means that it's less likely we are going to get a deal," he tells the BBC.

BBC Scotland correspondent Lorna Gordon says while there has been no official comment from the Palace, these will be "uncomfortable days" for the relationship between the government and the monarchy.

"While the Queen has no leeway in prorogation – she has to follow the advice of her ministers and prime minister – the whole system of a constitutional monarchy is predicated on politicians not doing things that expose the Queen to criticism or even question," she says.

Laura Kuenssberg
BBC political editor

This judgement was just about as bad for the government as they could have dreamt in their worst nightmare.

By any normal comparison this is a terrible defeat for the prime minister which could do great damage to his reputation.

But remember we are not in normal political times.

People inside Boris Johnson’s bunker believe this judgement could, in time, help them make the case they are trying to put to the country at large – that he is the only person who is absolutely determined to get Brexit done, whatever the cost.

And anyone standing in the way – whether it’s opposition MPs or the judges in the Supreme Court - they only add to that impression of him trying to battle these obstacles to try to keep his promise.

But to say that strategy is a gamble is a serious understatement.

It is ruthless, perhaps - risky certainly – but don’t rule out more audacious moves.