Ukip Rochester and Strood win latest in line of shocks
Ukip's success in the Rochester and Strood by-election is the latest in a history of mid-term ballot-box shocks.
Others in recent decades include:
1962 Liberal Eric Lubbock, now Lord Avebury, took the London suburb of 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 that 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 October 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 Tory seat on a 25.3% swing while Clement Freud polled 38.3% to win the Isle of Ely from Conservatives 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 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 World 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 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 barely 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 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 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 rocked 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%.
2009 Tory Chloe Smith became the youngest MP when she snatched Norwich North from Labour on a 16.5% swing.
2012 Respect's George Galloway took Bradford West off Labour on a 36.6% vote share turnover. However there was a boost for Labour later that year when its candidate Andy Sawford won Corby from Tories on a 12.7% swing.
2014 Ukip returned its first elected MP after Tory Douglas Carswell resigned to force a by-election at Clacton which he fought under his new party's banner. He won with a 12,404 majority compared with his 2010 General Election margin of 12,068 for Conservatives.