Which Witch?

Arriman the Awful, Wizard of the North, is tired of being the most evil wizard in the world. He decides he must get married and produce a son to take over from him. His wife must be an enchantress of the highest powers, and witches galore enter his sell-casting competition. Belladonna has no chance. She's not even hideous, flowers spring up on her pillow as she sleeps, and bats nest happily in her hair. She longs to be a fiendish hag and win the competition - but how? An outstandingly clever and funny children's novel that was runner-up for the Carnegie Medal.