A small district in London discovers an ancient treasure and learns that it is part of Burgundy. They try to be independent of Britain.
An unexploded bomb in Pimlico is going to be blown up. Arthur Pemberton (Stanley Holloway) presents his model for a new swimming pool to the council meeting and sees children cause the bomb to explode. Arthur falls in the hole and finds a gold coin. Arthur and his daughter Shirley Pemberton (Barbara Murray) explore the cave and find buried treasure.
Parents persuade their children to take responsibility for the explosion. Professor Hatton-Jones (Margaret Rutherford) testifies that the Duke of Burgundy claimed the land in the 15th century, and the local people own it. The banker Wix (Raymond Huntley) claims that Pimlico is Burgundy, and word spreads. He estimates the value of the treasure at 100,000 pounds. People dance and tell the police that it is a foreign country.
Police tell the local people that they have been withdrawn from Pimlico. Arthur calls the Home Office and learns that they need a committee of elected representatives. So they have a meeting and elect Arthur, Randall, and Spiller. The Duke of Burgundy (Paul Dupuis) arrives and gives his papers to Arthur. Hatton-Jones meets with the Duke and asks if he is a bleeder.
English customs officers begin inspecting those leaving Pimlico. Later a train is stopped while Arthur and others inspect the passengers. Hatton-Jones recognizes the authority of the Duke of Burgundy. In the evening he kisses Shirley.
Arthur learns that the English are closing the frontier, and the nineteen families are facing a siege. The electricity goes off. Molly Reed stores their food, and the Duke supervises communal feeding. Wix says they will keep their treasure, and Prime Minister Arthur says they will build the swimming pool.
Only a little water is left, but at night they get water from a fire hydrant and fill the hole. Shirley left the taps on, and their place is flooded. The people of Pimlico gather to surrender, but children and others throw them food. Arthur tells Straker (Naunton Wayne) and Gregg (Basil Radford) that he wants to negotiate; but they say they have no power to do so and leave.
A newsreel reports that the English people are divided over the Burgundy issue, and talks begin. Gifts continue to be sent in by helicopter and parachutes. Wix proposes lending money to Britain. Straker and Gregg attend a banquet by the pool, and Arthur announces that they are back in England.
This political satire reflects the rebuilding of political
structures and economic recovery in Europe after the devastation
of World War II. Even a small group of people who organize themselves
for action can be a movement that challenges a big government.