Side elevation of 1 Trevor Square, Knightsbridge, from Trevor Street. Trevor Square and adjoining streets were laid out on the site of Powis House, the late seventeenth-century mansion of the Trevor family. The architect William Fuller Pocock developed the estate, and laid out Trevor Square c1819-21. Number 1 is a brick three-storey house standing at the north end of the square adjoining Trevor Street. It has a basement, mansard, stucco to ground floor and iron railings at street level and was Grade II listed in 1970, listing number 1066204. The building is being refurbished, with a temporary roof structure covered in tarpaulin. Number 8 Trevor Street lies next door, part of a terrace of three-storey houses developed by Pocock at the same date as the square. 8 Trevor Street was Grade II listed in 1970, listing number 1066212. It has a sign marked 'Price' at a first-floor window, presumably advertising an estate agent or similar. A Fiat 124 sedan is parked on the street with a Simca 1501 Tourist estate behind it. 1 Trevor Square lies within the Knightsbridge conservation area designated in 1968, and is still extant, as are the houses in Trevor Street.