In the newspapers of the time, the vast majority of references to 'nightwatchman' refer to someone employed to look out for incendiary bomb fires in all manner of establishments, eg. factories, schools, cinemas, townhalls.
It is worth noting that Cheltenham had a particular problem with this threat and in 1941 a number of new measures were taken as a result, including the Home Guard working with the Fire Brigade and others concerned with civil defence, additional Auxiliary Fire Service recruits, and the use of nightwatchmen.