Father B. U. Gormless, S. J. is a priest and author who is credited with the Principle of Double Intent, discovered in 1952, and discusses it in his book, Mental Reservations and Other Traps (Saint Fidgeta and Other Parodies, 46).
Gormless (chiefly Britain, of a person): Lacking intelligence, sense or understanding; foolish.
The priest's initials spell BUG which may have been a joke of Bellairs's. The S.J. denotes the priest is a Jesuit.