Biggest % point increases in gov party vote share in post-war Westminster by-elections:

7.3 (Lab, Preston 1946)
8.5 (Con, Copeland 2017)
8.9 (Lab, Hull N 1966)
9.8 (Con, Barnsley 1953)
12.0 (Lab, Bournemouth 1945)

23.0 (Con, Hartlepool 2021)

— Matt Singh (@MattSingh_) May 7, 2021