D A Young (Derek Anderson Young) wrote just the one pony book that I have been able to find: Ponies in Secret. It is unusual in being illustrated in colour throughout, with colour plates and a frontispiece by Maurice Tulloch. It’s a pity the author didn’t write more. This story of a family hugely excited by the prospect of a summer holiday with ponies, which then fizzles when they meet the teenage heads of the local riding club (drunk with power, in my opinion) is a well observed story of the wielding of power, and of how easy it is to misinterpret what people do.
Finding the book
Ponies in Secret is becoming harder to find, and more expensive.