Born in Islington, the son of distinguished neurologist Macdonald Critchley, CBE (1900–1997) and his first wife, midwife Edna Audleth (née Morris), Critchley was brought up in Swiss Cottage, North London, and in Shropshire, where he attended Brockhurst School, a preparatory school in Church Stretton, and later Shrewsbury School.