MB ChB Aberdeen 1955, MD 1964; FRCP 1974; DPM Eng 1961.
Lascelles was chief assistant to the department of neurology at Guy's Hospital, resident medical officer at the National Hospital, London, and registrar to the department of neurology and psychology at St Thomas's Hospital, London. In the early 1970s Lascelles was appointed senior consulting neurophysician at MRI and honorary lecturer in neurology at the University of Manchester. Lascelles was a fellow of the Royal Society of Medicine.