In United Kingdom constitutional law, prorogation is an act usually used to mark the end of a parliamentary session. Part of the royal prerogative, it is the name given to the period between the end of a session of the UK Parliament and the State Opening of Parliament that begins the next session. The average length of prorogation since 2000 (i.e. calendar days between the date of a new session and prorogation of the previous Session) is approximately 18 days.[1] The parliamentary session may also be prorogued before Parliament is dissolved. The power to prorogue Parliament belongs to the monarch, on the advice of the Privy Council.[2] Like all prerogative powers, it is not left to the personal discretion of the monarch but is to be exercised, on the advice of the prime minister, according to law.[3]