As always with his work, Roald was very thorough in the planning, as these extracts from the archive show. Here, he illustrates exactly how Mr Hoppy's ingenious plan of 'growing' Alfie the tortoise should be carried out, noting at the top of the page:
"There are nine tortoises in the following illustrations. Each of them from No. 1 to No. 9 should get progressively larger by one-eighth so that No 9 is exactly twice the size of Alfie."
The BBC One film adaptation of Esio Trot starring Judi Dench and Dustin Hoffman will be shown at 6.30pm on New Year's Day.