Three Men in a Boat (1975)
Last night I watched a delightful version of Three Men in a Boat from 1975!

This is, of course, based on Three Men in a Boat (To Say Nothing of the Dog) (1889) by Jerome K. Jerome.
The screenplay is by Tom Stoppard. It is directed by Stephen Frears.
It stars Tim Curry, Michael Palin, and Stephen Moore— sadly, I can find no mention of who plays Montmorency (the dog).
This was so fun to watch! I'm oh so glad I came across it!