P. C. G. Cazalet s. of Sir Peter Grenville Cazalet (1929-2019) [see
http://announcements.telegraph.co.uk/deaths/233210/cazalet] and (m. 1957) Jane Jennifer Rew.
Per Who's Who and Kelly's Handbook 1969: Sir Peter Cazalet s. of Vice-Adm. Sir Peter Grenville Lyon Cazalet (1899-1982), K.B.E., C.B., D.S.O., D.S.C., Commander of the Reserve Fleet, and (m. 1928) Elise, dau. of James Percival Winterbotham, of Cheltenham. The elder Sir Peter was son of Grenville William Cazalet, of Bexhill, Sussex, L.R.C.P., M.R.C.S.
I couldn't find G. W. Cazalet in BLG 1969, and BFI gives another family (undoubtedly connected) of the name, 'of Alderton House', as appearing in BIFR 1958, which I don't have.
Per BMD records, G. W. Cazalet b. 1860, d. 1947; m. 1897, Edith Louisa Lyon. His father appears to have been another Peter Grenville Cazalet (1813-1862), s. of Peter Reade Cazalet and his wife Caroline. A Peter Reade Cazalet d. 1839; a Peter 'Beade' Cazalet, parents William and Mary (see below), was christened in 1781.
The BLG 1969 pedigree gives a William Cazalet (1749-1795) who m. Mary Reade (-1812), of Waddon, Sussex, 'leaving issue' (William was the eldest son, the pedigree continuing with the issue of the fifth, Noah), these presumably being the parents of Peter Reade Cazalet as above.