Experts have been answering questions posed by readers.

"Can the PM veto the extension bill?" asks Ian in Wakefield.

Maddy Thimont Jack, from the Institute for Government: "The bill is going to become law tonight, and then the PM is going to have to follow the law. It basically says that if a deal or no deal hasn't been approved by 19 October, the PM needs to go to Brussels and ask for an extension. The bill also says that if all 27 EU members states agree to the request - the bill says it must be by 31 January 2020 - then the prime minister must also agree to that extension."

BBC Reality Check's Chris Morris: "People have also been asking can the PM use loopholes to get around it? The lawyers I've spoken to say you could try, but if this goes to court, then the government will lose. That's because the law of the land - and once Royal Assent is given, it is the law."

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Former Tory Dominic Grieve - who lost the party whip last week - said he was "sorry to have to move this motion as it ought not to be necessary to do so".

He said when he was Attorney General, he had to advise on "propriety" in government.

"We are very blessed... as within government there was a deep understanding that for our largely unwritten constitution to function, there has to be a high level of trust," he adds.

"My concern is there is increasing and compelling evidence this trust is breaking down and there is cause to be concerned whether conventions are being maintained."

There was a lot of shouting and disagreement on whether the debate (requested by Dominic Grieve) should go ahead, but John Bercow wasn't having any of it.

He addresses someone on the government benches as a "footling member".

And then he says...

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Jeremy Corbyn now makes his application for an urgent debate on the rule of law, amid concerns No 10 may seek to get round new legislation which aims to block a no-deal Brexit.

He says there is "very deep concern" about the government's commitment to comply with the law, which had royal approval earlier this afternoon.

John Bercow also approves Jeremy Corbyn's application.

He says it will take place for up to an hour and a half, beginning immediately after the emergency debate led by ex-Tory MP Dominic Grieve.

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John Bercow approves the urgent debate application - and, after more than 40 MPs stand up to support it, he confirms it will take place now, for up to two hours.

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The former Tory Dominic Grieve says the prorogation of Parliament meant there is "much which is left undebated".

He points to two things in particular: not having the opportunity to ask questions of government in relation to its no deal planning, and its "motives" in suspending Parliament.

He therefore wants to have a debate about seeing the detail.

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The Speaker is now listening to the application for an urgent debate from ex-Tory MP Dominic Grieve on the legal advice ministers received about the Parliament suspension, plus the Operation Yellowhammer no-deal planning documents.

Mr Grieve wants to use a parliamentary device known as a "humble address" to the Queen to force the publication of letters, emails, and text messages between ministers and advisers.

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After nearly an hour and a half of tributes to John Bercow, points of order finally come to an end.

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A number of MPs have used points of order to criticise the Leader of the House, Jacob Rees-Mogg.

The Tory MP came under fire last week for saying a doctor who has concerns about medical supplies post-Brexit was "as irresponsible as Dr [Andrew] Wakefield", who inaccurately linked the MMR vaccine with autism.

Mr Rees-Mogg later apologised in a statement, but did not make an apology to the Commons - where he made the statement.

Lib Dem Dr Sarah Wollaston and shadow health secretary John Ashworth both called for an apology from the dispatch box.

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Leader of the Liberal Democrats, Jo Swinson, joins the swathes of MPs paying tribute to John Bercow in the Commons.

She says: "To those outside, Parliament can appear stuffy and out of touch.

"Some of the initiatives that have come in on your watch... means when people are talking about issues outside this place, we can be discussing them in a timely way."

Ms Swinson says she was "moved" by his tribute to his wife and children, saying many MPs' families "put up with a lot".

She adds the he is "an unstinting guardian of parliamentary democracy at a time when people feel the need to take to the streets to argue to defend our democracy".

Parliament is due to be suspended later, just days after MPs returned from the summer recess.

Known as prorogation, the closure will follow a High Court ruling that the prime minister's decision was "not an unlawful abuse of power".

So, why is it happening?

Read more here.