These National Vigilance Association (NVA) files were originally prefixed with the letter 'S' and a number from '1' onwards, each number representing a subject, and the files of that subject were then given a letter from 'A' onwards - thus 1A, 1B, 1C, etc.
Some of these files (particularly 1/NVA/4/1/11) cover international as well as British matters.