WEB5 days ago · The Commonwealth Secretariat residential property, the Garden House, 40b Hill Street, Mayfair, London, W1J 5NT. The property is the official residence of the Commonwealth Secretary General, it is a mid-terrace five storey house located in Mayfair, the floor area of 744.38 sqm (8,013 sq. ft) on a gross internal area (GIA) basis.