Why is Parliament suspended, how long is the suspension and why was it ruled unlawful?

BORIS Johnson's suspension of Parliament was met with outrage by MPs who accused the PM of pushing through the "father of all lies".

But what is prorogation, and why has the Supreme Court ruled it unlawful? Here's the latest.

Why was Parliament suspended?

Boris Johnson suspended Parliament on September 9, vowing to push through Brexit by the October 31 deadline.

The PM defended the controversial move, saying the five-week suspension until October 14 would allow the government to set a new legislative agenda.

But he was accused of lying to the Queen in gaining her permission to dissolve the House and faced several court appeals.

A Scottish court first ruled his suspension was unlawful  and "stymied" justice, but an English court it lawful.

The matter was then brought to the Supreme Court to deal with two appeals, one from campaigner Gina Miller, and the other from the government.

Mrs Miller was appealing against the English High Court's decision that the prorogation was "purely political" and not a matter for the courts.

The ruling was made after a three-day hearing at the Supreme Court last week which dealt with two appeals - one from campaigner and businesswoman Gina Miller, the second from the government.

The government had been appealing against the ruling by Scotland's Court of Session that the prorogation was "unlawful".

Why was it ruled unlawful?

A three-day ruling resulted in the Supreme Court finding the prorogation "unlawful and void" in a historic ruling on September 24.

Lady Hale returned the unanimous verdict of behalf of all 11 justices.

She told the Supreme Court that the move to shut down Parliament with just weeks to go before Brexit "took place in exceptional circumstances" and his decision was "extreme".

"The House of Commons has a right to a voice," she said.

"No justification for taking action with such an extreme effect has been put before the court.

"The Court is bound to conclude, therefore, that the decision to advise Her Majesty to prorogue Parliament was unlawful because it had the effect of frustrating or preventing the ability of Parliament to carry out its constitutional functions without reasonable justification."

The ruling comes as a huge blow to Johnson, who had vowed to deliver Brexit by October 31.

MPs have now been instructed to return to Parliament tomorrow, while Boris Johnson prepares a hasty return from the UN Climate Summit in New York.

What does proroguing Parliament mean?

Parliament is suspended for times throughout the year anyway - like the summer holidays right now.

But to prorogue Parliament means to completely shut one parliamentary session and start a new one.

MPs won't come to the Commons for a period of time before having a new Queen's Speech, and the start of the next session.

Until then, MPs are on a so-called break.

The speech is a list of laws the government plans to get approved over the year – for Boris this could include a number of policy changes he hopes will win him voters in the case of an election.

When Parliament doesn't sit - either because it's suspended or prorogued - it's harder for Remainers to push through anti-Brexit legislation or use obscure parliamentary tricks to block our divorce from Brussels.

What happens when Parliament is prorogued?

The Prorogation of Parliament is the formal name given to the period between the end of a session parliament and the "State Opening" of Parliament that begins the next session.

Prorogation brings to an end nearly all parliamentary business, but public bills may be carried over from one session to the next.

It means all MPs will have a short break before being allowed to come back and debate new laws.

Responding to the Speaker John Bercow's previous announcement that another vote on Brexit cannot be brought forward, some MPs suggested proroguing Parliament for a short period of time.

The Queen formally prorogues Parliament, on the advice of the Privy Council, before an announcement is read in the House of Lords on her behalf.

Had it been done before?

Centuries ago, prorogation was used on a whim by the sovereign to suit their own interests.

For instance, summoning Parliament so it could authorise taxes, and proroguing it to limit its activities and power.

In the nineteenth century, prorogation was a big deal - monarchs would arrive in great processions and give the prorogation in person.

However, this tradition ended in 1854 when Queen Victoria decided she would no longer attend in person as she disliked the ceremony.

From 1855, a prorogation speech, prepared by the Government, was read by the Lord Chancellor, and in 1867, Prime Minister Benjamin Disraeli introduced the custom of having the Lord Chancellor read the prorogation speech in the first person, as if the Queen were speaking the words herself.

This practice continues at Royal Commissions for prorogation today, the only difference being the speech is now read by the Leader of the House.

But even in modern times PMs do prorogue Parliament too.