The Silvertown by-election of 1940 was a wartime by-election.
Silvertown was a safe Labour seat, and none of the major parties stood against the Labour candidate.
It was one of the last by-elections contested by the British Union of Fascists where they campaigned on a platform calling for an immediate peace with Nazi Germany, a policy which won them only 151 votes.
References
Silvertown by-election, 1940 Wikipedia(Text) CC BY-SA