Alan has illustrated dozens of fantasy books, including some nonfiction, and many more covers. Several works by J.R.R. Tolkien are among his most notable interiors: the Tolkien centenary edition of The Lord of the Rings (1992), a 1999 edition of The Hobbit that has been boxed with it, and Narn i Chîn Húrin: The Children of Húrin (2007).
The latter, a first edition, is his work most widely held in WorldCat participating libraries.Other books he has illustrated include Faeries (with Brian Froud), Lavondyss by Robert Holdstock (as well as the cover of an early print of this book), The Mabinogion (two versions), Castles and Tolkien's Ring (both nonfiction by David Day), The Mirrorstone by Michael Palin, The Moon's Revenge by Joan Aiken, and Merlin Dreams by Peter Dickinson.
He has also illustrated retellings of classics for young people. Two were Rosemary Sutcliff's versions of the Iliad and the Odyssey—namely, Black Ships Before Troy (Oxford, 1993) and The Wanderings of Odysseus (Frances Lincoln, 1995). Another was Adrian Mitchell's version of Ovid's Metamorphoses—namely, Shapeshifters (Frances Lincoln, 2009).