Passport to Pimlico (1949)

The accidental detonation of an unexploded World War II bomb in Pimlico, London, England reveals a treasure trove. Residents find documents proving that the region is, in fact, part of Burgundy, France--ergo, it's foreign territory. The British government attempts to regain control by setting up border controls and cutting off services to the area, and the "Burgundians" fight back.