Winfield House
Winfield House is a mansion set in of grounds in Regent's Park, the second largest private garden in central London, after that of Buckingham Palace. Since 1955, it has been the official residence of the United States Ambassador to the United Kingdom. Wikipedia*
On the C-SPAN Networks:
Winfield House has hosted 1 event in the C-SPAN Video Library; the first program was a 1991 News Conference.