The 1940 Middleton and Prestwich by-election was held for the Middleton and Prestwich constituency on 22 May 1940, after the death of the sitting MP, Nairne Sandeman. It was held during World War II, and five of the largest political parties – Conservative, Labour, Liberal, National Labour and National Liberal agreed to an electoral pact not to contest any by-elections in seats held by any of the other parties.