Prorogation: How can the government suspend Parliament?
The controversial decision to suspend Parliament days after MPs returned to Westminster is to be challenged in the Supreme Court.
So, why did it happen?
Can the prime minister close Parliament?
The official term for shutting down Parliament is "proroguing".
MPs do not vote to prorogue - it's a power that rests with the Queen, done on the advice of the prime minister.
So, it is within Boris Johnson's gift to ask the Queen to shut Parliament, dramatically reducing the influence of MPs.
Even though the Queen agreed to the request, legal proceedings have been brought against the government, which will be decided by the Supreme Court.
How is Parliament normally closed?
Parliament is normally prorogued once a year for a short period - usually in April or May.
During this time, all business stops, so most laws that haven't completed their passage through Parliament die a death (although some may be "carried over" to the next session).
MPs keep their seats and ministers remain in position - but no debates and votes are held in Parliament.
This is different to "dissolving" Parliament - where all MPs give up their seats to campaign in a general election.
It is also different to a recess - a break in the Parliamentary session - which was due to take place this year from roughly 13 September to 8 October.
So, in theory, prorogation only loses MPs up to seven parliamentary days. But, unlike recess dates which MPs get to approve, they were not consulted.
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It is normal for new governments to shut down Parliament, in order to hold a Queen's Speech, which sets out its plans for the next year or so.
The length of time varies - in 2016 Parliament was closed for four working days, while in 2014 it was closed for 13 days.
This year, Parliament will be suspended for 24 working days before the new Queen's Speech on 14 October.
While prorogation is normal, the timing of it in this case is "clearly hugely controversial", says Maddy Thimont-Jack, of the Institute for Government think tank.
Why is it controversial?
As well as reducing the influence of the elected Parliament in a major decision, it could also make planning for the possibility of no-deal Brexit harder.
That's because the prime minister - without a sitting Parliament - will not be able to pass laws to cushion the impact of no deal. Such laws, for example, might deal with allocating extra money or resources.
It also brought the Queen right into the Brexit dispute. Normally, a prime minister's request to the Queen to prorogue is extremely straightforward. In fact, the House of Commons Library says it has been a formality in the UK for more than a century.
The government has defended the decision, saying that proroguing Parliament to enable a Queen's Speech will allow the PM to address domestic policies like NHS funding.
Opponents, on the other hand, say it is undemocratic. When the decision to prorogue was first made public, many MPs were concerned it would limit the time available to find ways to block a no-deal Brexit.
However, despite having less Parliamentary time, MPs succeeded in passing a law that seeks to extend the Brexit deadline.
Could prorogation be stopped?
Former Conservative Prime Minister Sir John Major joined forces with anti-Brexit campaigner Gina Miller, to challenge the advice the PM gave to the Queen.
However, on 6 September High Court judges rejected the case.
In contrast, a separate case saw Scotland's highest civil court rule that the suspension of the UK Parliament is unlawful.
Despite calls for Parliament to be recalled, the government has said that Parliament will remain prorogued, pending an appeal.
This will be heard by the Supreme Court.
So could the government be ordered to reopen Parliament?
The Supreme Court will consider whether the decision to prorogue was lawful or not and has the final say.
If the judges rule that prorogation is legal, then Parliament will remain shut until 14 October - unless the government advises the Queen to change the date.
Ms Miller's lawyers are, however, asking the justices for a repeat of the declaration from Edinburgh's Court of Session that the PM's actions were "null and void and of no legal effect".
If her side wins, it's still unclear how and when Parliament would resume - whether MPs could simply return to the Commons, or if they would need to be recalled by The Queen on the advice of Mr Johnson.