A half-century of by-election upsets
Previous shock results included:
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. It was a bad year for Conservatives, who lost Rochdale to Labour, coming third.
1962: Liberal Eric Lubbock, now Lord Avebury, took Orpington off the Tories on a 26.8% swing.
1966: Gwynfor Evans gave Plaid Cymru its first seat when he took Carmarthen from Labour on an 18% swing.
1967: Winifred Ewing snatched a seat for the Scottish National Party, when she turned a 16,576 Labour majority at Hamilton into a 1,799 nationalist one. She polled 46% in a constituency previously uncontested by her party.
1968: Tories chalked up a 21.1% swing to take Dudley on March 28 from Labour as well as marginal Meriden and Acton. This was possibly the first time in history a party lost three seats at by-elections on the same day.
1969: Liberals captured Ladywood, their first Birmingham seat for 83 years, from Labour on a 32% swing. The two years from November 2 1967 to Oct 30 1969 brought Labour its worst by-election run. The party lost 10 seats during that time and the swing against it was never less than 10%.
1972: Liberals overturned a 12,696 Conservative majority to win Sutton and Cheam on a 32.6% swing.
1973: Labour defector Dick Taverne won Lincoln for the Democratic Labour Party, standing against his former party and polling 58.2%. At Ripon Liberal David Austick gained the seat on a 25.3% swing while Clement Freud polled 38.3% to win the Isle of Ely for the party - which had not fought the constituency in the 1970 General Election. The SNP's Margo MacDonald gained Glasgow Govan from Labour on a 26.7% swing.
1976: Tories gained Walsall North on a 22.5% swing after the imprisonment of former Labour minister John Stonehouse.
1977: The Conservatives toppled Labour in its Ashfield mining stronghold on a 20.8% swing.
1979: David Alton turned a Labour majority of 6,171 in Liverpool Edge Hill into a Liberal lead of 8,133, achieving a 32.4% swing.
1981: Shirley Williams, a Social Democratic Party founder member, won Crosby from Tories on a 25.5% swing for the Liberal/SDP Alliance. Liberal Bill Pitt ousted Conservatives at Croydon North West on a 24.2% swing.
1982: But in the last days of the Falklands War it was Tories' turn to win when they took Mitcham and Morden off 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 Tories on what was the last occasion the Government party gained an Opposition seat at a by-election.
1983: Liberal Simon Hughes gained the highest swing since the Second Word War - 44.2% - when he won Bermondsey from Labour.
1987: Just months from the General Election the SDP's Rosie Barnes stormed Labour's Greenwich, south London, stronghold, winning with a 16.1% switch.
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 before.
1989: Labour's John Smith took the Vale of Glamorgan from the Tories on a 12.4% switch - giving the party its most dramatic by-election win for more than half a century.
1990: The "safe" Conservative seat of Mid-Staffordshire was won by Labour with a 21.3% swing. Liberal Democrats ended a run of disappointing performances when they captured Eastbourne from the Tories on a 20% switch.
1991: Liberal Democrats captured Ribble Valley, among the top 15 Tory strongholds, by notching up a 24.7% swing after a campaign dominated by the poll tax. Labour also triumphed two months later winning Monmouth from the Tories on a 12.6% move. Key issue here was the National Health Service.
1993: The first by-election of the new parliament saw Liberal Democrats capture 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 Liberal Democrats.
1994: Tories were forced into third place at Eastleigh, where they were defending a 17,702 majority. Liberal Democrats gained the seat on a 21.4% swing with a 9,239 majority over Labour. The year ended with Labour scoring its biggest swing for nearly half a century, 29.1%, to take Dudley West from Tories.
1995: Conservatives were forced into third place by Labour as the SNP took Perth and Kinross off them on an 11.5% swing. Just over a month later they also tumbled to third position as Liberal Democrats took Littleborough and Saddleworth on an 11.6% swing.
1996: Tories went down to Labour in another landslide at Staffordshire South East where the votes movement was 22.2%.
1997: With the General Election less than two months away, Conservatives lost to Labour at Wirral South on a 17.2% swing. Tories failed to win a single by-election between William Hague's victory at Richmond, Yorks in 1989 and their success in the first contest of the new 1997 Parliament at Uxbridge.
But this success was short-lived when Liberal Democrat Mark Oaten won the Winchester poll, a re-run after the General Election result was declared void, with a 21,556 majority on a 19.8% swing.
2000: 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. This was the first time for 35 years that Tories had lost a seat at a by-election in Great Britain when they were in Opposition at Westminster.
2003: Labour suffered its first Commons by-election loss since it returned to power in 1997 when Liberal Democrats snatched Brent East, north London on a 29% swing.
2004: 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, Scotland on a 16.2% swing in the next door constituency to that of the, then, Chancellor Gordon Brown.
2008: Mr Brown, now Prime Minister, was shaken by Tories' first Commons by-election gain in more than a quarter of a century when they took Crewe and Nantwich on a 17.6% votes turn-round. Two months later Glasgow East became the second so-called "safe" seat lost by Labour on Mr Brown's watch. The switch to the Scottish National Party was 22.5%.
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