It took place on the same day as the Labour defeat in Ashfield. The result in Grimsby and Ashfield were seen as a surprise as they were the opposite of what had been expected. Grimsby had been expected to fall to the Conservatives, while Labour had expected to hold Ashfield, which they had held by a much larger majority. In the event while there was a swing of 20.9% to the Conservatives in Ashfield, which was just enough to win the seat, the Labour to Conservative swing in Grimsby was only 7% and Mitchell managed to poll more votes than Crosland had at the last election. The Liberal Party lost its deposit in both Grimsby and Ashfield, the third time this had happened at a by-election following the 1977 Lib-Lab Pact.
