The Bishop of Winchester was granted lands in the vicinity of Farnham in 688. The castle at Farnham was created by Henry of Blois, Bishop of Winchester (1129-71) and Abbot of Glastonbury (1126-71). Henry was a grandson of William I, and brother of Stephen. This castle was demolished in 1155 during the reign of Henry II (who had been crowned in December 1154).
The present shell keep, surrounding the original castle on its mound, dates to the late 12th century. Remains of the original square tower can be seen at the centre of the motte. The castle then became home of the bishops of Winchester, including William of Wykeham (in 1368), and Thomas Wolsey (in 1529).
The castle was captured by parliamentary troops under Sir William Waller in December 1642, and then became a garrison.
The Church of England Diocese of Guildford was formed in 1927, and the castle continued to be an official residence until 1955. The castle keep was placed in state care in 1933, and is now a property of English Heritage. Sir Charles Peers had hoped to acquire the keep in 1912.
The official blue guide was written by Michael Welman Thompson, who served as Principal Inspector of Ancient Monuments for Wales. Thompson conducted excavations at the castle from 1958-60.
Thompson also wrote the official Ministry guidebooks for Pickering Castle (1958), and Conisborough Castle (1959), Kenilworth Castle (1977), as well as the National Trust guide for Tattershall Castle (1974). For Thompson’s Yorkshire guidebooks see here.
The present English Heritage guidebook, containing colour illustrations, is by John Wareham. In spite of its title (Three Palaces of the Bishops of Winchester) it covers four palaces in the care of English Heritage:
- Wolvesey (Old Bishop’s Palace), Hampshire
- Bishop’s Waltham Palace, Hampshire
- Farnham Castle Keep, Surrey
- Winchester Palace, Southwark, London
Heritage Futures 
You have a very well written and interesting piece here. I love castles.