Per 192.com, it would appear that Mr Hartley Russell's third christian name is Desmond. He is of the Russell of Bucklebury family, which, per Burke's Family Index, last appeared in Burke's Landed Gentry in the 1952 edition.
The article on the Russell family in BLG 1952 only gives their male line descent; the Bucklebury estate, however, came to them through the female line, via the Winchcombe, Packer, Hartley and de Palatiano families (see http://buckleburyestate.com/bucklebury-history/).
The Russells of Bucklebury are of the same family as the Russell baronets of Littleworth Corner, having a common descent from Charles RUSSELL (2 I 1759 - 28 X 1828) of Killough, County Down. By his first wife (married 1 IX 1784), Rose M'COY (died 9 VII 1785), this gentleman had a son, Arthur RUSSELL (9 VII 1785 - 28 V 1845), who was the father of Charles Arthur RUSSELL, Baron Russell of Killowen, GCMG, PC (10 XI 1832 - 10 VIII 1900), the first of the three Russell of Killowen Law Life Peers, and the progenitor of the Russell of Littleworth Corner baronets.
The aforementioned Charles RUSSELL, of Killough, was married secondly to Anne McEVOY, by whom he had a further five sons and five daughters. One of the sons, Thomas RUSSELL (died 16 II 1868), also of Killough, was the father of Charles William RUSSELL, JP (1837 - 14 V 1891) of King's Castle, Ardglass, County Down, whose marriage in 1876 to Frances Oxenham Henrietta Santa DE PALATIANO (1846 - II 1918) brought the Bucklebury estate into the Russell family. They were the great-grandparents of Robin Derek de Palatiano Howard ("Willie") HARTLEY RUSSELL, MVO, DL, who is High Sheriff of the Royal County of Berkshire for 2021 to 2022.
Felix Hartley Russell's maternal grandfather, Simon Matthew Dudgeon OLIVER (per company records, born on 22 July 1940), is the brother of Gabriel(le) Georgina Sybille OLIVER (born 1944), who in 1964 (registered Q3 - Surrey South East) was married to, as her first husband, Eamon Vincent O'MEARA (c.1934/5 - 7 III 1966), by whom she had a younger son, Piers Stefan O'MEARA (born 30 III 1965).
Piers Stefan O'MEARA took his stepfather's surname after his mother's second marriage in 1967 (registered Q3 - Surrey South West) to (Anthony) Glynne PUGHE-MORGAN (born 1941); he is better known as the former newspaper editor and television personality Piers Morgan.