He was born in 1916 in Islington, London to Edie and Joseph Clark. His mother was a seamstress and his father a shop assistant. He went to Highbury Grammar School on a scholarship. An article in the News of the World encouraged his teenage interest in hiking, which he did initially in the Chiltern Hills and in Surrey. He passed the London County Council exam and began a career in local government for the Council and then the National Health Service. He joined the Youth Hostel Association in 1937. During World War II he was assigned to a non-combat role, having been refused registration as a conscientious objector; he was posted to Hereford and the Welsh capital, Cardiff, where he began a youth hostel club. He hiked in Wales and the Marches. He met a like-minded partner, Isobel Hoggan, through the YHA. On their first date, the couple watched the passage of the National Parks and Countryside Act in Parliament in 1949, on which Clarke had worked. They married in 1952 and lived in Guildford and later near Godalming. Hoggan was a committed feminist; both became active Quakers and vegetarians. Clark's passion was for the countryside. He joined the YHA executive committee in 1948; he was national treasurer and then chairman till 1963. He worked for the general public to gain access to land e.g. working for the National Trust as their YHA representative, the Campaign for National Parks and the Open Spaces Society, the latter from 1978 as commons liaison officer and he was vice-president at the time of his death. He toured widely on his scooter to view potential acquisitions for the National Trust. He supported and argued for the Trust's founders' emphasis on protecting the landscape, rather than ownership of buildings thereon. In 1967, his tact and diplomacy avoided a schism at the Trust and he was on the committee which drove through a change to a more inclusive organisation. Through his influence, the moorland plateau of Kinder Scout in Derbyshire and the archaeological and environmental resources of the Abergwesyn Commons in Wales were purchased by the Trust. After a 40-year effort, his campaign for the South Downs to become a national park was successful. He was the chair of the YHA and the National Trust's southern regional committee, voluntary director of the Samaritans in Guildford, a member of the Department for Transport's advisory committee and a member of the Campaign for State Education. From 1983 to 1986, he was secretary of the Common Land Forum whose recommendations were passed to the Government. For his 100th birthday, the National Trust planted trees in his honour at its site at Polesden Lacey, Surrey. He was awarded their founders medal and was appointed a CBE for his conservation work. His wife, Isobel, died in 2016. Clark's memoirs were published in 2018. He died in 2019, aged 103; he is survived by his sons – Alistair, Stuart, and Neil – and his grandchildren.
