Image source, Reuters

Boris Johnson's advisers could continue to "stress test" the British constitution in the coming weeks, says businesswoman Gina Miller, who led campaigners against the suspension of Parliament.

"What is so alarming is that [the prime minister] is willing to stress test our constitution," she says.

"[He and his advisers] are acting in a way that is very unconstitutional... in a way which is really going to carry on testing, I think, our system and our stability over the next few weeks."

She adds that MPs must now scrutinise the prime minister "from tomorrow up until whenever it is we leave or don't leave".

Radio 4 PM

Labour peer Lord Falconer, a former Lord Chancellor, tells BBC Radio 4's PM programme that today's judgement is "the very first time that a court has told the prime minister how he should relate to Parliament".

He says it's an "absolutely gigantic day in the constitution" but denies that it shows the UK needs a written constitution to settle debates about the powers of government.

"Surely it shows that when someone behaves as badly with the constitution as Boris Johnson has done, the full weight of the law will fall upon him?"

The Conservative Party should take action and hold Boris Johnson "to account", shadow chancellor John McDonnell says.

Labour will talk with other opposition parties in the House of Commons tomorrow, he adds, to discuss questioning Mr Johnson in Parliament about his behaviour.

"We will see what answers we receive from him and then consider with other opposition parties what the next steps are," he says.

However, he adds that the "onus" is on the Conservative Party to make a decision about Mr Johnson's premiership: "I think the Conservative Party should act."

Radio 4 PM

Rory Stewart, a Tory leadership candidate who was expelled from the Parliamentary party for rebelling on Brexit, tells BBC Radio 4's PM programme that this is "the end of the no-deal Brexit strategy".

He says the prime minister and his allies have to recognise that Parliament is sovereign and there is no majority for leaving without a deal.

"We need to get out of this mad, Trumpian world" where MPs refuse to compromise, he says.

Mr Stewart says Liberal Democrat plans to stop Brexit without another referendum and Brexiteer calls to "ram through no-deal" would "split the country down the middle".

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Boris Johnson's government made an "absolutely catastrophic political judgement" when it prorogued Parliament, Brexit Party leader Nigel Farage says.

"I think he's in trouble, I think he's in real trouble," he says.

"The prospects of leaving on 31 October have completely evaporated."

He adds that the most likely outcome is an extension to Brexit - which he says the UK would request at a summit in Brussels on 17 October - followed by a general election.

Boris Johnson has blown apart grey areas of the UK constitution, highlighting the role of the monarch.

Jeremy Corbyn has finished his conference speech to resounding applause. He ended with a plea to go forward and win an election "for the people of this country".

BBC political correspondent Chris Mason got the final lines:

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The court's ruling does not prevent Mr Johnson from proroguing again, as long as it does not stop Parliament from carrying out its duties "without reasonable justification".

So if Mr Johnson wants a Queen's Speech on 14 October (as originally intended), he could prorogue Parliament a few days beforehand so that preparations can be made.

Read more about the Queen's Speech and would happen if MPs voted it down

Image source, PA Media

At a joint press conference with President Donald Trump in New York, the first question from reporters is whether Boris Johnson would resign.

"As I said earlier on, let's be absolutely clear. We respect the judiciary in our country, we respect the court," he says.

"I disagree profoundly with what they had to say. I think it was entirely right to go ahead with a plan for a Queen's Speech.

"Frankly we need to get on with Brexit. Whether they voted to Leave or Remain they want to get this thing done by October 31 and that's what we're going to do."

President Trump criticises the reporter for asking the question. "That was a very nasty question from a great American reporter," he says.

But Mr Johnson defends the media, saying: "I think he was asking a question, to be fair, that a lot of British reporters would've asked."

Mr Corbyn says: "We need to get Brexit sorted and do it in a way that doesn't leave our economy or our democracy broken.

"The Tories want to crash out without a deal and the Liberal Democrats want to cancel the country's largest ever democratic vote with a parliamentary stitch-up."

He says if Labour win an election “it will be the people that win”.

Mr Corbyn says Labour is the only party to give the people the final say on Brexit, because “Labour trusts the people”.

He says that a Labour government would renegotiate a Brexit deal within three months and give people another referendum within six months of being elected.

He pledges to carry out "whatever the people decide".