Well, let's just say I had some time on my hands while waiting.
To most Americans, the film is all but unknown, save for fans of The League of Gentlemen, where it features in a sketch about Kenny Harris' movie theater that features only films featuring dogs. Here he speaks with his competitor (played by a pre-Doctor Who Chis Eccleston)
Dougal Siepp: Kenny Harris. As I live and breath. Are you not out of business yet Kenneth?
Kenny Harris: Quit carping Siepp. We do DVD and video rental now. Do you know what my biggest title is?
Dougal: I'm sure you're going to tell me.
Kenny: Digby. "Digby the biggest dog in the world." Can you rememeber what you said about it?
Dougal: Funnily enough, no.
Kenny: You said it were dated. No-one would want to see it in this day and age. 17 rentals in 20 weeks, explain that!It's rather a national guilty pleasure in England. It was featured as first day programming on two separate independent television channels, and back in the day, with only one hand's worth of channels, everyone watched.
One of the things that amazes me about the film is the cast - it's a who's who of TV and character actors. The male lead is Jim Dale, already popular from a run of the Carry On movies, and shortly before his move to America for a series of Disney films and of course, Barnum on Broadway. The rest of the cast is equally impressive - Spike Milligan, Milo O' Shea are two big names. The film shares a great number of cast members with Beatles films - Victor Spinetti (In both Hard Day's Night and Help!) plays a scientist, Norman Rossington (their put-upon manager in HDN) and John Bluthal (Bhuta, Klang's assistant in Help!) play a pair of inept burglars, and the film was produced by Walter Shenson, who produced HDN. There's a great many TV actors as well, including Bob Todd and Henry McGee from Benny Hill's repertory company, Frank Thornton (Captain Peacock from Are You Being Served) All this crossover only serves to support my theory that there are only about 57 actors in all of Britain, which is why everybody gets a chance at anything. The film was written by Michael Pertwee (Jon's brother) from a novel by Ted Key, creator of the Hazel comic strip. Ted also wrote three of Disney's live-action films, including Million Dollar Duck, Gus and The Cat from Outer Space.
The plot is rather simple - Billy White (Richard Matheson) adopts Digby, a (normal-sized) English Sheepdog. His mom (Angela Douglas) is a scientist at a top-secret installation, and when his grandfather refuses to allow the dog in the house, they pawn him off on Jeff Eldon (Dale), a fellow scientist, specializing in animal psychology. The science team are working on a growth serum to help grow vegetables quickly for manned space flights. It works all too well - the vegetables won't stop growing - a 50-foot long cucumber is paraded by as evidence. Jeff decides it wouldn't harm anyone if he nicks a bit of the formula to help his roses grow, and wouldn't you know it, the dog ends up eating it instead.
Jeff has to keep the pachydermic puppy a secret from the other scientists and from little Billy, and plans to take him to his Aunt Ina's farm. Before he can, he attracts the attention of criminals Tom and Jerry who plan to steal him and sell him to a circus. After a fun scene at a cafe so dodgy the silverware is chained to the table (providing a nice bit of physical comedy for Dale), they succeed. After a photo Digby appears on TV to publicize his appearance, both Jeff and Billy recognize, and both set off to save him. Digby escapes both their grasp, and he makes his way across the countryside leaving kid-friendly destruction in his wake.
The army is eventually brought in, and Jeff and Billy have only seconds (okay, quite a bit of time, really) to feed Digby a hastily-prepared antidote to bring him back to animal companion size. Not to ruin the film, but this is a kids' film, and the film does end with a giant-sized animal chasing the romantic antagonist across the British countryside.
The effects for the film are pretty good for the time, a combination of miniature sets and rudimentary matte work. The main problem the film has is that Digby doesn't actually DO much - he sits about a bit, barks in slow motion, and only nearly causes mayhem when he either sits on a train track for a bit, or quietly ambles across an airport runway. The animals in the film also don't quite seem that well trained. Dale has several scenes with a chimp named Clarissa who looks like she's going to reach out and rip his jaw off at any minute.
I hasten to add that some years later, the Weekly Reader offered the novelization for C.H.O.M.P.S., but this time I refrained. Once bitten and all that.