Not so easy, it turns out. Bedknob and Broomstick has only existed since 1957. It was a combining of the earlier The Magic Bedknob with Bonfires and Broomsticks. So if Danny's book has that title, it can't be earlier than 1957, so "Valiants" could be a revision referring to the 1950s aircraft. What we need is to check a first edition copy of The Magic Bedknob, of which three are available on AbeBooks.I think this is unlikely too, but it might be easy to discount.
Anyone got a spare £85?