Rex Dixon is credited with stories in Swift Annual 1962 (1961) and 1963 (1962); the first of these was published anonymously but is easy to identify.
The author's real name was Reginald Alec Martin (1900-1971), whose first published novel, a western for adults, appeared in 1949. During the 1950s and 1960s, he turned out some 114 novels for adults and children as well as ghosting a couple of non-fiction titles for sportsmen. His two main fields were westerns and science fiction and he is probably best known for his Pocomoto adventures (as Rex Dixon) and the Kemlo science fiction novels (as E. C. Eliott).
I mentioned that his contributions to Swift Annual were easily identified because both featured Pocomoto, 'Just Lucky' (1961) and 'The Mustang' (1962). There is a very good summary of the Pocomoto novels written by Jim Mackenzie as well as lots of illustratoins from both the Pocomoto and Kemlo series on John Tipper's Reginald Alec Martin page at the Collecting Books and Magazines web site.
The picture above comes from Swift Annual 1963 and is drawn by Harry Bishop and is © Look and Learn Magazine Ltd.