The by-election was caused by the death of the sitting MP Dame Cheryl Gillan. Although the Liberal Democrats were the clear challengers a win for them was by no means certain; the Conservative government remained popular and had gained a seat off Labour at the Hartlepool by-election the previous March. The uncertainty was reflected in calls for an electoral pact between Labour, Liberal Democrats and Greens by former LibDem MP Philip Lee and Guardian columnist Polly Toynbee. A number of issues including HS2, the government’s proposed planning reforms and uncertainty as to what levelling up meant for the South of England provided ammunition for the Liberal Democrats which ran a strong campaign with Liberal Democrat leader Ed Davey visiting the constituency no less than 16 times. Sarah Green is the first Liberal MP elected in Buckinghamshire since Lady Vera Terrington in 1923.