What do people in the United Kingdom commonly call the location of the room where the entire play "On the Rocks" is set?
On the Rocks (play):  The entire play is set in the Cabinet Room of 10 Downing Street. 10 Downing Street: 10 Downing Street, colloquially known in the United Kingdom as Number 10, is the headquarters of the Government of the United Kingdom and the official residence and office of the First Lord of the Treasury, a post which, for much of the 18th and 19th centuries and invariably since 1905, has been held by the Prime Minister.
Number 10