Clancey served in the 51st (Highland) Division with the Allied forces in Sicily and Italy during World War II, narrowly escaping death and being deafened in one ear by an artillery explosion.

Clancey wrote extensively about the taxonomy of African birds, naming some two-hundred sub-species of Southern African birds.

• The Birds of Natal and Zululand (1964);
• The Gamebirds of Southern Africa (1967);
• Catalogue of the Birds of the South African Subregion (1965–1972);
• Handlist of the Birds of Southern Mozambique (1970–1972);
• Co-author of Vol II of Atlas of Speciation of African Birds (1978);
• Chief Editor of the S.A.O.S. Checklist of Southern African Birds (1980);
• The Rare Birds of Southern Africa (1985);
• Kingfishers of Sub-Saharan Africa, Publisher: Jonathan Ball Publishers (31 December 1992)
• The Birds of Southern Mozambique. Publisher: African Bird Book Publishing;
• Contributed to The Atlas of Southern African Birds (1997).