Many of the incidents and characters in the book and movie were based on real-life events and people from author Roald Dahl's own life. For example, he knew a butcher who taught him the art of poaching, and Captain Lancaster (Ronald Pickup) was based upon a real and similarly-vicious teacher --- identified as "Captain Hardcastle" in Dahl's childhood-autobiography book, "Boy" --- whom Dahl had while in school; like the teacher in the book, Captain Hardcastle was ex-military and still arrogantly wanted to be addressed as "Captain", even though it was a very low rank and the war was long over; also like the fictional character, he obsessively kept an eagle-eye on his pupils to seek out opportunities to punish them, and had the creepy fire-colored hair and mustache, watery eyes, and shell-shock-caused twitching and grunting.
In this movie, William and Danny's surname is Smith. In the book, William and Danny's surname is never given. Conversely, William's late father was named Horace in the book, but, while he is mentioned several times in this movie, his name is never given.
The movie was filmed entirely on-location in Oxfordshire, England. Much of the filming took place in Stonor Park, the house on which is used as the location for Victor Hazell's mansion.
This movie omitted several book characters, the most obvious omission being Charlie Kinch, the local taxi driver who helps Danny and William with the heist and drives them to a place to stash the pheasants. Other characters omitted are Miss Birdseye and Mr. Carrado (the local Pre-School and Primary School teachers, respectively; these characters are mentioned by the same names in Dahl's childhood-autobiography book, "Boy"), as well as the Headmaster's wife Mrs. Snoddy and the shopkeeper Mr. Cooper (replaced by Mr. Wheeler who is an amalgamation of the book characters Mr. Cooper and Mr. Wheeler).
Samuel Irons (Danny) is the real-life son of Jeremy Irons (William Smith) and grandson of Cyril Cusack (Doc Spencer). The idea to cast Samuel in this movie was Jeremy's own idea. They had just finished acting together in a production of "A Midsummer Night's Dream", and Jeremy thought the experience of a movie set would be good for Samuel.