No.12 and Attached Railings

This is a house dating from approximately 1790 to 1793, with alterations in the 19th and 20th centuries, designed by John Palmer. It is a group value building. The front is constructed of limestone ashlar, with rubble to the basement and limestone ashlar and rubble at the rear. The roof is a double-pile mansard with Welsh slate, a coped gable wall to the left, and ashlar stacks at the front; the rear stacks are not visible.

The house has three storeys, an attic, and a cellar, with a three-window front. The first floor has three 19th-century plate glass sash windows in splayed reveals, and the second floor is similarly designed. The ground floor has two matching sash windows with stone sills to the left, and a six-panel door with flush and raised and fielded panels, alongside a 19th-century iron knocker and decorative fanlight within a round-headed opening. The basement has two six/six-sash windows with a continuous stone sill, a plank door with overlight set within ashlar infilling, and 20th-century area steps. A double dormer features plate glass sashes. Other exterior details include a band course over the ground floor, a wrought-iron balcony with a rosette design and iron slat floor supported by six iron brackets set into the band course, a moulded eaves cornice, and a coped parapet. The rear elevation has a six/six-sash window to the ground floor, 19th-century windows above, and a mansard constructed in ashlar, along with a small, single-storey ashlar extension with an artificial slate roof.

The interior was not inspected during the listing process.

Attached to the house are railings and a gate with urn tops on limestone bases. The property was originally part of an incomplete development of St James's Square on land leased in 1790; the upper part of Park Street was begun to Palmer's design and continued by John Pinch after 1808, but was never fully completed. The street was formerly terminated by All Saints Chapel and was intended to extend northwest as Regent Place.