Lesley King wrote just the one book, as far as I know. It was written while she was fifteen, and still at school. The title, The Horse from the Moor, is a bit of a puzzle: I assume it comes from the fact that one of the equine heroes, Starflleet, is a moorland breed, but I couldn’t swear to this. The plot is pretty straightforward: the club members aren’t much good, but under Colonel Maxten’s tuition, they get better. There are a couple of flies in the ointment: spoilt new girl Christa Maclaine, and Pam’s complete inability to ride her horse Starfleet. There is a cast of thousands in this book, but unlike Josephine Pullein-Thompson’s Noel and Henry series, also with a cast of thousands, there is very little to differentiate the characters. Josephine Pullein-Thompson has the gift of making the most minor character memorable, but that isn’t true of Lesley King. Only three characters: Ginette, Pam and Christa, emerge with any clarity, and the Colonel is just a cipher. No Major Holbrooke here.
Much of the action is fairly run of the mill too: with the exception of Pam, everyone progresses at their riding quite steadily, and much of the book is simply a recitation of who came where in various gymkhana events. There are a lot of events in this book, and none of them are, alas, particularly exciting. The thing I found most interesting was the fictional breed of Minderley horses, but they’re only mentioned in passing.
Finding the book: it’s relatively cheap and easy to find.