I found this book in a little bookshop in Hay-on-Wye, a receptionless town in Wales that is basically just one huge bookshop. If you’re ever in Wales you should visit it. Even the coffee shops sell books.
Anyway, this book is by one T. A. Pratt and it is called Spell Games. Judging by the price in American or Canadian dollars on the back, and the fact I’ve never seen any of the author’s other books anywhere, I’d say the books have never really been marketed in Europe.