37 Upper Brook Street and attached railings

This is a late 1730s terraced town house, later rebuilt in 1907 by Maurice Hulbert of Matthews, Rogers and Co. for the Grosvenor Estate, and now used as offices. It is constructed of Portland stone ashlar, channelled at ground floor level, with a slated mansard roof and box dormers featuring prominent cornices, the central one being pedimented. The architectural style is a mid-18th century French and English Classical Revival.

The building is four storeys high, with an attic and basement, and has three windows to the front. A segmental arched doorway features double part-glazed doors with wrought iron grilles. Later 20th-century two-pane sashes are on the ground floor. The first floor has architraved casements with bracketted cornices, the central one with foliar drop enrichment and a cartouche above the cornice; a stone balconette extends the width of the front, with an ornate wrought iron balustrade featuring panels of foliated arabesques. The second floor has sashes with lugged architraves and aprons, with the central sash having foliar drops and a bowed sill. A projecting, bracketted cornice is located at the third floor sill level, where sashes are recessed and the central sash is flanked by moulded panels. The entablature is surmounted by a balustrade with urns. Elaborate 18th-century revival cast iron railings are attached to the front areas.

The interior is exceptionally complete, predominantly in the Louis XV style. A full-height open well marble stair has a Louis XV style cast iron balustrade, lit by a lantern with cast iron grilles. A servants' stair runs from the basement to the attic behind the main stair. An original Waygood Otis lift with its mechanism and timber panelled cage is also present. The ground floor front room contains a cornice and central medallion, along with a late Adam style marble chimney piece dating to circa 1780/90, featuring tapering pilasters inset with Siena marble strips and finely carved urns, and a re-used Georgian fireback. A rear room has a mahogany panelled dado and fireplace. A passage leads to a rear salon in a Wrennaissance style, with fluted Corinthian pilasters to oak panelled walls and an enriched plaster beamed ceiling. First-floor rooms, possibly dating to the 1920s, are separated by sliding and folding doors, with fielded panelling, enriched moulding, a coved cornice, and central plaster ceiling medallions. Window surrounds, overdoors, and mirrored overmantles are decorated with foliar and floral plasterwork. Similar white marble fireplaces are present in the front and back rooms. Doors with segmental arched heads lead to square-headed doorcases, with panelled jambs. Rear doors lead to a small landing with five marble steps and a balustrade matching the main stair, leading to a half landing. The second and third floor rooms also have good marble fireplaces. The rear second-floor bathroom features a dado, glazed tiles in a foliar Art Nouveau design, and a chequered tile floor. Basement corridors are tiled to full height, with a band of blue and white patterned tiles at dado level. It is a good example of the arrangement and style of a grander Edwardian town house.