UK — animorphs

The UK publisher Scholastic Hippo published Animorphs books #1-54, Megamorphs #1 and 2, The Hork-Bajir Chronicles, and The Andalite Chronicles. Books #47-54 were published as combined editions of 2 US books for each UK book: 47/48, 49/50,51/52, 53/54. Earlier printings of books had a more plain background (used for books #1-18) and later printings (including the later books #19-54 and reprints of #1-18) had more colorful striped backgrounds. The earlier printings of books #9,10,11,12,13 and Megamorphs #1 included collectible Character Cards, one character for each book. If you collected all six cards, they would spell a message when put together, and you could use that message to enter a contest to win a mountain bike and other prizes.

Earlier Printing covers

Earlier Printing back covers

Megamorphs and Chronicles Front and Back covers

Later Printing covers

Later Printing back covers

Character Cards

Trivia

If you look closely, you can see that the UK cover of the Hork-Bajir chronicles is slightly different from its appearance in the UK book back covers - Aldrea, the Andalite is looking toward the reader instead of away.
The trivia information on the back of the Character cards is the same or very similar to the text on the back of trading cards for each character given out as a promotional item for Megamorphs #1 in the US.
The book spines for the earlier printings had a picture of the character near the middle of the book spine, while for the later printings the character's picture was at the bottom.
If you look closely at the back covers of some of the earlier printings, you can see part of the morphed animal on the cover. For book #1, you can see the lizard, for #2 you can see the cat, for #3 you can see the hawk (side view), and for #13 you can see another view of the hawk (front view with wings spread). For the rest of the earlier printing back covers, they just show the same cloud pattern that is on the US books. The only book with a completely plain back cover is #5, which is the only book to have a different international cover morph (lobster) than the US cover morph (gorilla).