The FlatHomeLiving Room
Harry Pottle's design sketch from 1964 for Steed's third flat as seen in the book The Avengers and Me (1997), p.76.

Although the flat in the series looks different from this original design sketches, some elements remained, such as the the entrance door on a landing, the handrail and serveral steps leading to the main living area.

"Athmosphere was created with its furnishings and military memorabilia, enhanching Steed's character as the elegant, suave, ex-military gentleman and the apartment reflected 'club' style comfort and good taste.'(The Avengers and Me,S.76)
John Steed's Flats - No.3
4, Queen Anne's Court - Sketch