3 Stable Mews

1. The Wall Lamps

There are several matching wall lamps in Steed's flat. A pair of them can be seen to the left and the right of the mantlepiece, one right to the spiral staircase and another one at the left site of the guest room door. The lampshades have different forms and they have either green stripes (as in The Superlative Seven) or brown ones (as in The Joker)

At 3 Stable Mews John Steed does not have a study (at least not on this floor of his flat).
A mahogany desk stands at the right side of his living room, sometimes it is moved to the right wall of the flat as seen in Split! or Legacy of Death. The desk has seven drawers, in one of them, Steed can store Champagne with dry ice.

On the desk are several objects: an electric French Empire style lamp, a brass or bronze model of a mortar cannon (a sharpener?), a silver or marble cigarette or cigar box, a crystal or glass ashtray, a leather write wallet, two cut glass shakers with slaked sand, different telephones and often a box for notebook paper and a calendar.
Sometimes there is a small nautic Zodiac globe. It often stands in other places of the living room.

Unidentified drawings of parks or squares in London (?) and two paintings with whaling ships

Sometimes the prints can be seen in the kitchen, sometimes at the wall with the storage room.
The one below on the right snapshot is an engraving from Ambroise Louis Garneray for Herman Melville's Moby Dick and I guess the upper one is also a painting of Garneray.

The tuba was in Steed's possession since series 3 episode Dressed to Kill. Two different tubas can be seen in his fourth flat; the left one got destroyed by a bomb in Something Nasty in the Nursery. Since series 6 Steed had plastic flowers in his tuba, one time the tuba is empty (Stay Tuned) and it leaked in Get-A Way!
The instrument is only a decoration, and a vase for flowers as Steed can't play the tuba (Take Me to Your Leader). The only other musical instrument which can be seen in one of Steed's flats is a clarinet in Death of a Batman and elder Steed owns a piano and a violine. But only Mike Gambit and Purdey play the piano.

Steed is a collector of militaria. He owns several musketries and long guns which have their place in the living room next to the entrance door and at the wall behind dining table opposite to the kitchen. He's also collecting medals and military decorations, and cap badges. One could see a similar collection in series 3 episode The Nutshell in Steed's second flat. A small collection of two to four flintstone pistols is placed right to the mantlepiece in the living room. Steed bought a replica of a 17th- century single flintstone pistol in The White Elephant for 200 guineas.On the mantlepiece stand two model cannons which were used on British naval ships. It's a model of a cannon from the year 1672 (Requiem). There already was a larger one in his second flat next to the windows, and two stood in front of the mantlepiece. A "life-size" cannon of that kind can be seen in the QQF office in Honey for the Prince.

Over the years Steed became a collector in porcalain (TNA Dead Men are Dangerous). He already owned a few figurines in the third series of The Avengers and obviously started to collect military porcelain figurines from 1965 on. They are figurines from the Napoleonic Wars, but it's hard to say who the manufacturer is.

The two figurines on horseback at the bookshelf next to the kitchen are French Marshal Bessières (upper) and French Marshal Soult. The manufacturer of the figurines is unidentified, there are some famous such as Scheibe-Alsbach, Sitzendorf or Bourdois et Bloch, but the sockets of the horse statues do not match.

Inside the living room are severals seats
Steed's desk chair (two different chair were in use), two large dark red leather armchairs, the burgundy 3-seater Chesterfield, which does not match the armchairs in colour and the seat behind the entrance door, a red porter's chair.