The Tories’ loss of the long-held Chesham and Amersham seat will send ripples through Westminster and will go down in political history as the 14th biggest swing in percentage points against an incumbent party at a byelection. Here are some of the biggest political upsets when voters have gone to the polls outside of a general election: 1. Bermondsey, 1983: 44.2% swing from Labour to Liberal The biggest swing ever was achieved by the Liberals in 1983 when their candidate Simon Hughes, standing in a Bermondsey seat held by Labour with 63.6% of the vote in the general election four years earlier, won with 57.7%. Labour’s candidate was Peter Tatchell, now a prominent LGBT+ rights campaigner, who at the time faced vicious personal attacks over his sexuality. 2. Clacton, 2014: 44.11% swing from Conservative to Ukip A huge political upset came when Ukip gained its first MP in the form of the Tory defector Douglas Carswell. Having switched parties, Carswell promised voters in the Clacton constituency he had held since 2010 that he would trigger a byelection to ensure his mandate remained upheld. He won with 59.7% of the vote, a higher percentage than he got in the previous general election as a Tory, and far outstripping the new Conservative candidate, Giles Watling, who got 24.6%. Some months later a second Tory MP, Mark Reckless, defected to Ukip and also achieved a big swing when he fought a byelection, taking the party to 42.1% in Rochester and Strood, a seat in which it had not stood in 2010.
3. Hamilton, 1967: 37.9% swing from Labour to SNP There was a surprise victory for the Scottish National party in Hamilton after the Labour MP Tom Fraser quit the House of Commons for a new job. Having been a safe Labour seat, Hamilton elected the first candidate the SNP had stood there, Winnie Ewing. In a three-horse race she took 46% of the vote to Labour’s 41.5%, with the Tories trailing on 12.5%. Although the seat returned to Labour at the general election three years later, Ewing’s win marked the starting point of the SNP’s unbroken run of representation in the Commons. 4. Bradford West, 2012: 36.6% swing from Labour to Respect Labour temporarily lost the Bradford West seat it had held for decades when George Galloway stood, taking his Respect party from 3.1% at the 2010 general election to 55.9% less than two years later, a result he branded the “Bradford spring”. The constituency’s ethnically diverse electorate played a significant role in the campaigning by Galloway, who did not deny putting out a leaflet about which candidate was said to be more of a Muslim. Imran Hussain, picked by Labour to fight the seat after the previous MP, Marsha Singh, fell ill, achieved 25% of the vote. 5. Christchurch, 1993: 35.4% swing from Conservative to Liberal Democrat Robert Hayward, the Tory candidate in Christchurch after the previous Conservative MP died in office, suffered the greatest swing against a party that was in government at the time of the byelection. In the middle years of the John Major government, the seat was taken by the Lib Dems’ Diana Maddock with 62.2% of votes, up from the party’s 23.6% performance at the general election a year earlier. Labour also contested the seat and only managed 2.7%, while Alan Sked, before he founded Ukip, achieved 1.6%. • This article was amended on 24 June 2021 to remove a reference to 1993 being “in the final years of the John Major government”; Major was prime minister from 1990 to 1997.