The buildings
A map of 1815 is the earliest evidence of a house on the site of Kingswood Warren – it is called Old Warren House. Brayley’s Topographical History of Surrey (1845) says ‘The mansion has recently been much improved under the direction of Mr T.R. Knowles…’ The resulting house is shown in an engraving dated 1841. The central tower and the main entrance are immediately recognisable from Kingswood Warren as we see it today. The western part of the house, to the left of the tower, has been much altered – in the engraving it is of two storeys and lower than the part to the right of the tower, whereas today it is of three storeys and higher than the part to the right. However, the wall to the left of the house, with the entrance to what was presumably a kitchen courtyard, can still be seen behind the trees.

The reconstruction of the western part of the house was done by Sir John Cradock Hartopp and his architect William Bassett Smith. The shield on the front bay window shows the Hartopp arms, and the Cradock arms can be seen on the wall behind the trees. The monograms on the gable ends are those of Sir John and his wife Charlotte Frances, and the date 1873 can be seen on the rainwater-heads. As well as providing an extra storey of bedrooms, the rebuilding gave a double-height dining room with a serving-room and kitchen adjoining.

The outside of the mansion shows many other changes. The conservatory that can be seen to the right of the 1841 engraving has gone, replaced by a billiard room. The east front, facing the croquet lawns, seems to have been rebuilt – it is faced in stone, rather than the cement rendering with stone dressings on the rest of the house, and its bay windows are out of keeping with the gothic style of Alcock’s house. On the north side, a grand bay window seems to have been added to what was the library: it bears the Bonsor arms, and the associated rainwater head is dated 1899. The many-windowed bay on the north-east corner may also be a later addition. On the north-west corner there are several stages of extensions to provide more domestic offices and servants’ bedrooms.

When the BBC bought the house in 1948 there were already a number of outbuildings to the west: an engine house and battery room to supply electricity for lighting, a boiler house, a squash court, and greenhouses. The BBC built a new block (‘B Block’) in 1950, a new boiler house, and various extensions. The former coach house and stables, by the present main entrance, have been converted for offices and a workshop.

Internally there is little remaining from Alcock’s house. The reception hall and what is now the Oak Room have sometimes been one room, sometimes two. The Louis XVI panelling and plasterwork of the Cedar Room suggest a date towards the end of the nineteenth century, when French styles came back in vogue. The fine oak carving in the dining room includes the arms and monogram of Cosmo Bonsor, so is later than 1885. It is mentioned in an inventory of 1906, which also describes the dining room and the hall as having oak-beamed pitch-pine ceilings; so the ornate plaster ceilings that are such a feature today were presumably installed by Rank after 1912. In 1906 there were two principal stair-cases, one each side of the hall; the vanished one by the Cedar Room served only the suite of rooms on the east side which are now linked to the remaining staircase by a passage that partially divides the hall from the Oak Room. In the last few years, the main reception rooms of the mansion have been restored (the Cedar Room was a laboratory for many years) for use as a conference suite for national and international technical meetings and demonstrations.