In Ealing's Passport to Pimlico (1949), part of Pimlico turns out to belong legally to which historic duchy?

Passport to Pimlico is a 1949 British comedy made by Ealing Studios, directed by Henry Cornelius and written by T. E. B. Clarke. In post-war London, an unexploded bomb detonates in Miramont Gardens, Pimlico, and the blast uncovers a buried cellar holding artwork, coins, jewellery and an old manuscript. That manuscript is the royal charter from Edward IV, and it turns part of Pimlico into a legal part of Burgundy, exempt from postwar rationing and other bureaucratic rules. The film sets a small group against the British government and recalls the unity of wartime London. Stanley Holloway and Margaret Rutherford head the cast. It was nominated for the Academy Award for Writing (Story and Screenplay), which went instead to Battleground. The story is set during the heatwave Britain had in 1947, yet the filming itself took place during a wet summer in 1948.