Hodsoll played a major role in the development of air raid precautions [ARP]/ civil defence and this is reflected in the collection held at Churchill Archives Centre which he described as representing "a unique history of Civil Defence and its allied problems" (letter to Stephen Roskill, 27 August 1967). Until 1935 Sir John seems to have kept very few papers, but from then onwards very little of importance is missing. The printed material is particularly important because it consists of ephemeral pamphlets and reports now difficult to trace and copies of books presented to Sir John on publication. Among the typescripts the long series of reports are invaluable and may be the only surviving copies in many cases.