Avebury Manor and Garden

The house has had many extensions and changes over the centuries, including the addition of a racquets court in the 18th century,[10] the final addition being the West Library which was added by the family of Leopold C. D. Jenner who occupied the house in the early 20th century and completely redesigned the gardens.[8][11] The house was leased and restored by Alexander Keiller, heir to the James Keiller & Son marmalade business, who took an intense interest in Avebury henge in the late 1930s.[12]

In 1955 the rate of destruction of country houses had reached its peak, at one house every five days. The fate of Avebury Manor was in serious doubt when Keiller, whose excavations of the henge had been ended by the outbreak of war in 1939, put it up for sale. Few at the time were interested in the national heritage and the prospects for the manor were bleak. At this point Sir Francis Knowles stepped in and purchased Avebury Manor from Keiller. The Times described Knowles as "a fundamental scientist of outstanding calibre".[13] He immediately set about the restoration of the house which became an absorbing love as he learnt much about its construction, and claimed to have uncovered the signs of Gothic arches in the north east corner which had been filled in during Elizabethan times.[14] The family lived partly in cottages on the estate and partly in the house over the following three years, as the works progressed with substantial financial help from the Ministry of Works.

In May 1956, the house was amongst the first of the smaller houses to be opened to the public. In 1958 it was designated Grade 1.[8] In 1948 Knowles had married Ruth Jessie Brooke-Smith, the daughter of the Rev Arther Brooke-Smith. They brought up a large family at the manor: one son, Charles Francis (b. 1951) who later succeeded to the baronetcy, and three daughters, as well as a stepdaughter born to Ruth and her first husband, Dickie Hulse, an RAF fighter pilot killed in action during the Second World War.

The Knowles children recall it as a magical place in which to grow up, with acres of space to roam. They helped in all aspects of the early years of rather amateurish historic house tourism: using a surplus World War II field telephone between the tour guide (often an au pair with a vivid imagination) and the ticket office, serving teas, and helping themselves to coins from the wishing well to buy ice-creams from Sumbler's, the butchers just outside the gates. "Many would remember Francis as a most excellent host. Particularly memorable, however, was his hospitality at his beautiful Elizabethan house at Avebury, where he and his wife, Ruth, entertained so many people"."[15] Set against this background, remote from academic biology, he appeared to one of his colleagues as 'a fascinating man who would really have been more at home in the eighteenth century'. To another he gave proof that 'one could be both a distinguished scholar and a warm, vibrant person'.[16]

By 1974 the rate of destruction of the country house had come to a near standstill. This was due not just to stricter application of legislation, but also the high-profile Destruction of the Country House exhibition held in 1974 by the Victoria and Albert Museum. Having preserved the house for future generations, Knowles died suddenly on 13 July of that year in London, at the age of 59. He is buried in the churchyard of St. James Avebury, next to the house which he had lovingly restored to ensure its survival.

In 1976, Knowles' widow sold the house to Michael Brudenell-Bruce, 8th Marquess of Ailesbury.[3] After the Brudenell-Bruces left in 1981,[17] it was bought in 1988 by property developer Ken King, who caused local controversy by making changes without planning permission and opening an "Elizabethan experience" visitor attraction.[18] After King's bankruptcy the house was bought in 1991 by the National Trust.[17]