The creators made Wallace say "Wensleydale" because it made his face look nice and toothy. What they did not realize was that the cheese factory where Wensleydale cheese is made was on its last legs and was about to declare bankruptcy. Happily, this film's success brought the factory back from the brink.
Nick Park loosely based Professor Wallace on his own father, Roger Wulstan Park, who was an incurable tinkerer, inventor and architectural photographer. He once built from scratch a small trailer the family would take on trips to the beach. Park described it as a living room on wheels, complete with wallpapered interiors and wooden furniture bolted to the floor. Much like the rocket ship in A Grand Day Out.
This film took over six years to make, almost all of it single-handedly done by Nick Park himself. It formed part of his graduation project from the National Film and Television School, hence the co-production credit.
Gromit was going to originally be a cat, but then changed to a talking dog 'cause it was easier to animate, whose voice was recorded by Peter Hawkins. The idea of Gromit speaking and even him just having a visible mouth was completely scrapped when it became clear how expressive he could be just through small movements of the eyes, ears and brow, so no voices for Gromit were ever used.
Nick Park offered Peter Sallis £50 to voice Wallace, and his acceptance to record the part greatly surprised the young animator. Nicholas Wulstan Park wanted Wallace to have a Lancastrian accent like himself, but Peter John Sallis could only do a Yorkshire voice. Inspired by how Sallis drew out the word "cheese", Park chose to give Wallace a wide mouth and large cheeks (Wallace's head was originally thinner). When Park called Sallis six years later to explain he had completed his film, Sallis swore in surprise.