Technically, a member of Parliament is not allowed to resign their seat - but they can, by exploiting a loophole, voluntarily disqualify themselves from sitting in the Commons.
The loophole occurs because backbench MPs are not allowed to hold an office of the Crown, as this is seen to impose an unacceptable conflict of interest on the MP's ability to scrutinise the work of the government.
Two such offices, the Crown Steward and Bailiff of the Chiltern Hundreds and of the Manor of Northstead, have been retained for this purpose - even though they no longer burden the office-holder with any duties at all.
MPs can apply to the chancellor for these offices at any time, which are allocated alternately and held until they are passed down to another resigning MP.
On one day in 1985, 15 Ulster Unionists stood down at the same time in protest against the Anglo-Irish agreement.
One of the outgoing MPs, Enoch Powell, became Crown Steward of the Manor of Northstead until he was succeeded by Matthew Parris in April 1986.
If a member of the government wishes to resign from his or her government position while retaining their seat as a member of Parliament they must tender their resignation to the prime minister.
A resigning minister is normally entitled to make a personal statement in the Commons on the reasons for their resignation.
It is rare for cabinet ministers to resign from office and when it occurs it is usually embarrassing for the government.
This is because such resignations generally stem from a disagreement between the minister involved and the Prime Minister (such as Geoffrey Howe and Michael Heseltine), or from a personal scandal that has become public (David Mellor or John Profumo).
However, the effect of resignation can be reduced if the minister has threatened to resign repeatedly and cried wolf.
George Brown who eventually did resign in 1968 was said by Prime Minister Harold Wilson to have threatened to resign several times before it became a reality.
The sacking of a cabinet member is also embarrassing for the government as it is usually either due to disagreement between that person and the prime minister, or that person's failure in a particular job.
It is rare for a cabinet member to be sacked outright, they are usually offered the chance to tender their resignation first, or to jump before they are pushed.
A particularly fine example of this was the resignation of Selwyn Lloyd, who was chancellor of the exchequer between 1960 and 1962.
His letter of resignation to Harold Macmillan read: "You have told me that you would like me to resign and this I most willingly do".
Leaving the Party
Occasionally, members of Parliament may resign their membership of a political party due to disaffection with policy or personal disagreement.
For example, Clare Short left the Labour party in 2006, choosing instead to sit as an independent MP for the remainder of the Parliament.