The Englishman Who Went Up a Hill But Came Down a Mountain (1995)

Two English cartographers visit the small South Wales village of Ffynnon Garw, to measure what is claimed to be the "first mountain inside of Wales". It's 1917, and the war in Europe continues. The villagers are very proud of their "mountain", and are understandably disappointed and furious to find that it is in fact a "hill". Not to be outwitted by a rule (and the Englishmen who enforce it), the villagers set out to make their hill into a mountain, but to do so they must keep the English from leaving, before the job is done.