I have a very old, (1982) battered copy of this which I love. The pictures are weird and dark and it's interesting to compare them with his work in more recent years, where the weirdness is more benign.
However I was just looking on Amazon and the copy they have on has a different front-cover illustration.
www.amazon.co.uk/Naughty-Nigel-Puffin-Picture-Story/dp/0140554203/ref=sr_1_1?s=books&ie=UTF8&qid=1350137046&sr=1-1
I realised it's a picture illustrating an episode in the book where Nigel paints the cat and I suddenly wondered whether he'd re-done all the pictures because the originals were a bit freaky?
I can try and put a picture up if anyone wants to help me solve the mystery!