It was caused by the death in February of Anthony Crosland, and was retained for Labour by Austin Mitchell.
The result in Grimsby and Ashfield were seen as a surprise as they were the opposite of what had been expected.
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.
[1] 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.
This article about a by-election to the Parliament of the United Kingdom in England is a stub.