Prorogation (pronounced 'proh-ruh-gey-shuhn') marks the end of a British parliamentary session.

It is the formal name given to the period between the end of a session of parliament and the state opening of parliament that begins the next session.

The parliamentary session may also be prorogued before parliament is dissolved.

The monarch [in this case Queen Elizabeth] formally prorogues parliament on the advice of the Privy Council.

Prorogation usually takes the form of an announcement, on behalf of the monarch, read in the House of Lords.

It is made to both Houses and the Speaker of the House of Commons and MPs attend the Lords chamber to listen to the speech. The same announcement is then read out by the Speaker in the Commons.

The prorogation announcement sets out the major bills that have been passed during that session and also describes other measures that have been taken by the government.

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Prorogation brings to an end nearly all parliamentary business.

However, public bills may be carried over from one session to the next, subject to agreement. The first bill to be treated in this way was the Financial Services and Markets Bill in session 1998-99.

Following this, both the House of Commons and House of Lords are officially prorogued and will not meet again until the state opening of parliament, which marks the formal start of a parliamentary year.

The current session of Britain's parliament has been the longest in the history of the UK. It formally began on 21 June 2017 with the state opening, including the Queen's Speech.

A total of 798 days have since passed, making this the longest continuous parliamentary session since the UK was established by the Acts of Union in 1800.

The government announced the current session was to last two years to pass the key legislation needed to allow the UK's departure from the European Union.

More than two years later, the UK is still a member of the EU and the session still has not formally come to an end.

Prorogation in the second week of September would bring this current session to a close around the 810-day mark.

The previous record-holder was the session of 2010-12, which lasted 707 calendar days from the state opening on 25 May 2010 to prorogation on 1 May 2012.