If you were a pony obsessive in the UK, then you probably would have read Pony Magazine at some point. The early issues of the magazine rather went to town with their Christmas covers. Here's one from December 1950. I can't help but think that the horse on the right looks like a llama.
You can read more about Pony Magazine, and the Pony Magazine Annual, here.
Read more about the pony book in Heroines on Horseback, my survey of the world of the pony book from the 1930s onwards.You can buy a signed copy from me (I'll post them worldwide). The book's also available from the usual sources, or your local bookshop.