Here is a look back at some of the most memorable by-election results from the past 50 years.
1958: Mark Bonham-Carter gave the Liberals their first by-election gain since
1929 when he won Torrington, Devon, from Tories with a 219 majority.
1968: The Conservatives chalked up a 21.1 % swing to take Dudley on March 28 from Labour,
as well as marginal Meriden and Acton. It was thought to be the first time a party lost three seats at by-elections on the same day.
1969: The Liberals captured Ladywood, their first Birmingham seat for 83 years, from Labour on a 32% swing. Between November 2 1967 and October 30 1969 Labour lost 10 seats at by-elections.
1972: The Liberals overturned a 12,696 Conservative majority to win Sutton and
Cheam on a 32.6% swing.
1976: The Conservatives gained Walsall North on a 22.5% swing after the imprisonment of former Labour minister John Stonehouse.
1979: David Alton turned a Labour majority of 6,171 in Liverpool Edge Hill into a Liberal lead of 8,133, on a 32.4% swing.
1981: Shirley Williams, a Social Democratic Party founder member, won Crosby from the Conservatives on a 25.5% swing for the Liberal/SDP Alliance.
1982: In the last days of the Falklands War the Conservatives won Mitcham and Morden from former Labour MP Bruce Douglas-Mann, who had defected to the SDP, resigned his seat and stood again, pushing his old party into third place. There was a net 10.2% swing from Labour to the Tories on what was the last occasion the Conservatives won a seat off another party at a by-election.
1983: Liberal Simon Hughes gained the highest swing since the Second World War - 44.2% - when he won Bermondsey from Labour.
1988: Jim Sillars grabbed Glasgow Govan for the SNP on a 33.1% swing from Labour, emulating the victory in the same area of his wife Margo MacDonald 15 years earlier.
1989: Labour's John Smith took the Vale of Glamorgan from the Conservatives on a 12.4% switch - giving the party its most dramatic by-election win for more than half a century.
1991:The Liberal Democrats captured Ribble Valley, which had been thought to be among the top 15 Tory strongholds, by notching up a 24.7% swing after a campaign dominated by the poll tax.
1993: In the first by-election of the new Parliament, the Liberal Democrats took Newbury from Tories with 22,055 majority on a 28.4% swing. This was followed by the Christchurch contest which brought the biggest recorded swing against a government - 35.4% from Conservative to the Liberal Democrats.
1997: With the general election less than two months away, the Conservatives lost to Labour at Wirral South on a 17.2% swing.
2000: The Liberal Democrats took Romsey, next door constituency to Winchester, turning an 8,585 Conservative majority into one of 3,311 for themselves on a 12.56% swing. It was the first time for 35 years that the Tories had lost a seat at a British by-election while in opposition.
2003: Labour suffered its first Commons by-election loss since it returned to power in 1997 when the Liberal Democrats snatched Brent East, north London, on a 29% swing.
2004:The Liberal Democrats, benefiting from government unpopularity over the Iraq war, took another Labour seat at Leicester South on a 21.5% switch.
2006: Labour was rocked again by Liberal Democrats when they gained at Dunfermline and Fife West on a 16.2% swing. The constituency neighbours that of Gordon Brown.