In 1940, Alwyn decided to evacuate his family from their London house in Hampstead Garden Suburb to a small rented house in Welwyn Garden City in Hertfordshire. Alwyn was never called up – he claimed a heart problem caused his rejection from military service – and at night he became an air raid warden : listening, listening out – a vital warden's skill. In the ten-minute short Post 23 (1941) Ralph Bond introduces a group of air raid wardens, men and women from ordinary walks of life. They make their little speeches and are called out to a bombed-out house. Fires Were Started this is not, but its inspiration is similar. The film credited an “AR P [Air Raid Precautions] Adviser” – one W. Alwyn. This same W. Alwyn had a walk-on part as an extra – he appears briefly in a single shot (Plate 2), grinning all over his face, enjoying the lark. There is no reason to doubt that he was also responsible for the economical opening and title music : a bugle theme accompanied by plucked double bass.

By day William shared his time composing at home or travelling to the studios – sometimes to the ABPC studios in Welwyn. It must have been difficult. His son Jonathan clearly remembers “poor old father battling away with lengths that he had got to write in the rather small house we were renting … It was certainly the case that if father was on a major picture a great hush had to descend upon the house and my mother was inclined to say, you’ve got to work like anyone else – the rest of the house has to go on …” During the war, Alwyn produced an impressive amount of film music, although he was not always credited. Some 1400 official short films were produced throughout the Second World War. Since Crown and the government and armed service units could produce only 10%, the bulk was handled by independent companies, the best of which were also contracted to the Ministry of Information (MoI). Initially the documentarists were allowed only “non-theatrical” distribution : factory canteens, church halls, institutes, and 76 mobile cinema vans.