Swift and, presumably, also wrote their adventures for the Swift Annual. He was also the scriptwriter on "Cavendish Brown, M.D." for Eagle (1958-59).
Oddly enough, Nicky Nobody appeared in Swift Annual 3, but Bill Wellings wasn't listed as an author... however, one F. L. Wellings was listed that year and I suspect F. L. is related and might even be Florence Lydia Wellings (1910-1996), the only 'F. L.' I can trace in genealogical records.
Some further digging makes me now wonder whether Bill was William Ernest Welling, born in Walsall, Staffordshire, on 16 July 1907, who died in Cheltenham, Gloucestershire, in 1999. There's also a chance that Florence Lydia was his sister rather than (as I assumed back in 2006) his wife. Florence Lydia, born on 2 November 1910, had died in Gloucester, Gloucestershire, three years before. A Florence L. Wellings is recorded as born in West Bromwich, Staffordshire, in 4Q 1910.
Other than his comic strips, Wellings is credited with a single novel based on the Nicky Nobody character. It is probable that he is also the Bill Wellings credited with writing the "J.J." strip for the Sunday Express in 1962, drawn by Roy Dewar. If that is the case, it seems likely that Wellings was a freelance journalist who wrote comic strips on the side rather than a full-time comic scriptwriter.
Nicky Nobody and the Rocket Spies. London, Hulton Press, 1958.
(* The artwork is from Swift Annual 1962 (1961), drawn by Daphne Rowles. Nicky Nobody is © IPC Media.)