Fremlin was born in Kingsbury, Middlesex.
Fremlin was secretary of the Cambridge Scientists' Anti-War Group.
Responding to concerns about the use of poison gas bombs, he hosted experiments by the group in his room in Trinity College to determine the rate at which a gas might leak into a sealed room.
However Jack Haldane queried the rigour of his scientific methodology.
[3] This article about a physicist of the United Kingdom is a stub.