Basildon Park is a country house in Berkshire, between the villages of Upper Basildon and Lower Basildon. It is owned by the National Trust and is a Grade I listed building. The Dining Room is one of the rooms most frequently changed since the completion of the mansion. Yet today it closely resembles its original form. The original wall decorations, including panels, doors, mirrors and the fireplace, were sold in 1929 and are now in the Waldorf Astoria Hotel in New York.
For filming this scene, the room did not have to be emptied like for the ball scene with is filmed in the same room.
Behind the scenes: https://www.youtube.com/watch?v=sfI7nbH_Ocw