Chatwin was born on 13 May 1940 at his maternal grandparents' house in Dronfield, near Sheffield, Yorkshire. His mother, Margharita (née Turnell), had left the family home at Barnt Green, Worcestershire, and moved to her parents home when Chatwin's father, Charles Chatwin, went away to serve with the Royal Naval Reserves. He spent his early childhood living in West Heath in Birmingham (then in Warwickshire), where his father had a Law practice. He was educated at Marlborough College, in Wiltshire.