No. 10 and Attached Railings

No. 10 is a terrace house, built around 1790-1793, and later altered in the 19th and 20th centuries. It was designed by John Palmer and is now used as flats. The front of the building is limestone ashlar, the basement is rendered, and the rear is ashlar and rubble. It has a mansard roof covered with Welsh slate to the front and double Roman tiles to the rear, with a coped party wall and two ashlar stacks on the right, featuring early clay pots. A staircase is located at the rear.

The house has three storeys, an attic, and a basement, with a three-window facade. The first floor has three grouped sash windows: four/four panes, six/six panes, and four/four panes, with the left and right windows being narrower, set in splayed reveals. The second floor has three similar windows in plain reveals with a continuous stone sill. On the ground floor, to the right are two plate glass windows with horns, in splayed reveals and continuous stone sill; to the left, a six-panel door with beaded, fielded and glazed panels, alongside a cast iron wreath knocker, set within a stone doorcase with a 19th-century moulded architrave, incised pilaster strips with console brackets above, and a moulded cornice. There is one step leading to a pennant paved crossover with a cast iron footscraper attached to the doorcase. The basement has two nine/six sash windows in plain reveals and a continuous stone sill, alongside a 20th-century door with overlight in ashlar infilling below the crossover, and 20th-century area steps. A triple dormer is situated above with two plate glass horned sashes and a casement.

Other exterior features include a timber bressumer, a stone band course above the ground floor, a weathered sill band to the first floor, a frieze, a moulded eaves cornice, and a coped parapet. A lead hopperhead and downpipe are located on the right side. The rear elevation, partially visible, features six/six sash windows and a plate glass horned sash in a single dormer, with a lead hopperhead.

The interior was not inspected during the listing process. Attached to the property are wrought iron railings and a gate, with cast urn heads on limestone bases. The building is part of the St James’s Square development on land leased from Sir Peter Rivers Gay in 1790. Marlborough Street is one of the four diagonal approaches to St James's Square.