The biggest by-election swings in the last 30 years

The 25.2 per cent swing to the Lib Dems in Chesham and Amersham is the ninth largest of any by-election since 1991.

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The Liberal Democrats have surged to victory in the Chesham and Amersham by-election, turning a Conservative majority of 16,223 into a Lib Dem one of 8,028. The swing to the winning party of 25.2 per cent is the ninth largest of any by-election since 1991. 


The Liberal Democrats have a long history of by-election upsets – the party has been the beneficiary of five of the ten largest by-election swings in the last 30 years. 

The swing in Chesham and Amersham is the party’s largest since 2004, and surpassed the result achieved in Richmond Park, another affluent outer-London commuter seat long held by the Conservatives, in 2016.

The Liberal Democrats have long been the main challenger to the Conservatives in Chesham and Amersham, with the exception of the 2015 and 2017 general elections.

Labour won just 622 votes in the contest, its lowest vote share (1.6 per cent) in any by-election in history. The Green Party also failed to retain its deposit, winning only 3.9 per cent. 

Ben van der Merwe is a New Statesman Media Group data journalist. 

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