The Ponies of Britain society had its own magazine, which was first issued in 1957. It was edited by Glenda Spooner, who started Ponies of Britain with Gladys Yule. I haven’t yet found any covers that differ from the ones I have – all seem to have the same Joan Wanklyn illustration, just varying the excitement by having different background colours.
Each edition included a story, often by Glenda Spooner herself, show reports and profiles of well-known horses and ponies. The magazine used the best illustrators: besides Joan Wanklyn, John Tickner and Thelwell contributed. The great and good of the equine world contributed articles. I’ve found ones by Henry Wynmalen and E. Hartley Edwards.
I know many more copies of this appeared than I have been able to find, so if you can contribute any scans of missing editions I would be really glad to hear from you.