By-elections have provided a string of shocks which have reverberated through British politics.
They have upset the status quo, undermined key government policies, invigorated new political parties and brought fresh faces into parliament.
In three series of Triumphs and Disasters, broadcast on The Westminster Hour, the journalist and broadcaster Steve Richards remembers the contests which grabbed the headlines and talks to those who tasted success - and those who went red when the result was declared.
1991: The Ribble Valley by-election
Michael Carr won the by-election for the Lib Dems
It might have been one of the safest Conservative seats in the country, but in the Spring of 1991, the voters of the Ribble Valley were absolutely seething.
John Major had replaced Margaret Thatcher as Prime Minister six months earlier and this was the first electoral test of his premiership.
1990: The Eastbourne by-election
The Eastbourne by-election came in the dog days of the Thatcher Government - just a month before Mrs Thatcher was forced out of office.
But the election nearly did not happen. The vacancy was caused by the murder of the local Tory MP Ian Gow and there were calls for the other parties to give the Conservatives a clear run. But the election went ahead and resulted in a shock win for the Liberal Democrats, their first under the leadership of Paddy Ashdown.
1987: The Greenwich by-election
Greenwich was the by-election which revived the Social Democratic Party and undermined Labour, just four months before a general election. The winner, Rosie Barnes, remembers her moment in the spotlight.
1986: The Fulham by-election
Following the death of Conservative MP Martin Stevens, the by-election battle was in Fulham in west London.
Tony Blair wasn't even a member of the Shadow Cabinet then. But the discerning eye might have spotted the first glimmers of New Labour.
1983: The Darlington by-election
With a general election impending, the Darlington by-election was a huge opportunity for the SDP to do damage to the Labour Party. But their candidate turned out to be inexperienced - he called himself an amateur politician - and easy prey for the other parties and the media covering the campaign.
The Social Democrat candidate, Tony Cook, has rarely talked about the by-election he lost. He does for Triumphs and Disasters.
1981: The Warrington by-election
Soon after the formation of the Social Democratic Party, Warrington was the by-election the SDP lost - but claimed as a triumph.
Their candidate, the former Labour deputy leader Roy Jenkins, said, after losing to his former party by less than 2,000 votes, that this was "by far the biggest victory" he had ever been part of - because of the momentum it gave the SDP early in its life.
1977: The Stechford by-election
James Callaghan's Labour government has a majority of just one.
That made this Birmingham by-election , caused by the appointment of Roy Jenkins as a European Commissioners, more vital than most. Seventeen years later the same area of Birmingham, Hodge Hill, was to see another crucial by-election.
1973: The Lincoln by-election
Lincoln was the by-election which inspired those backing a centre party and foreshadowed Labour's furious battles between left and right. Dick Taverne re-lives his short-lived triumph for 'Democratic Labour', only to lose the following year to Margaret Jackson, now cabinet minister Beckett.
1967: The Hamilton by-election
Hamilton was the by-election which made the Scottish National Party a serious force in politics and helped put devolution on the agenda. The winner, Winnie Ewing, is among the interviewees.
1962: The Orpington by-election
Orpington was the by-election which breathed new life into the Liberal Party and wounded Harold Macmillan's Conservative government. Victor Eric Lubbock, now Lord Avebury, is one of those interviewed.
1938: The Oxford by-election
Neville Chamberlain with his piece of paper, returning from Munich
Just weeks after Neville Chamberlain returned from Munich, the voters of Oxford turned out in what had become a single-issue by-election: approving or rejecting the Conservative Prime Minister's peace strategy.
The Tory candidate Quentin Hogg held on in the face of a united challenge from the opponents of appeasement.