Whips are expected to maintain party discipline - mainly by encouraging MPs to vote according to the party line.
A to Z: Commons Whips
Each political party in Parliament appoints a team of MPs as whips.
Each of the two main parties will have about 14 MPs appointed to their whips' office.
The smaller parties may only have two or three whips.
There are also smaller teams of whips working in the House of Lords.
Whips also seek to ensure that all parties in the House of Commons are satisfied with the timetable of parliamentary business by communicating through the "usual channels".
Their unusual name is said to derive from the fox-hunting term "whippers-in" which is given to the rider at the rear of the pack of hounds who cracks the whip in order to keep any straying dogs in line.
Each whips' office sends a weekly note, known as "the whip", to their MPs indicating the level of importance of forthcoming votes.
Key votes on "the whip" will be underlined three times. These are known as "three-line whips" and members must attend.
If the whip is withdrawn as a disciplinary measure, an MP loses membership of their parliamentary party and is no longer sent party voting instructions.
Whips do not take part in debates in either the chamber or in committee, although there is a whip from each main party in the chamber during all proceedings.
Each party in Parliament has a chief whip who co-ordinates the work of his team of whips.
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