The 1962 West Derbyshire by-election was held on 6 June 1962 after the incumbent Conservative MP, Edward Wakefield, was appointed as Commissioner for Malta. It was retained by the Conservative candidate Aidan Crawley.
It is the largest loss of share of the vote suffered by the Conservative candidate, when the Conservative has still managed to retain the seat.
References
West Derbyshire by-election, 1962 Wikipedia(Text) CC BY-SA