Professor Hassell was honorary consultant rheumatologist at the Haywood Hospital Hospital, Stoke-on-Trent, for 24 years, until his retirement in September 2021. He was Head of the School of Medicine at Keele University, and, before that, was lead for the UK Rheumatology curriculum for several years. Since retiring as a full time clinical academic, he has taken part time posts as Keele University Academic Liaison lead for Sunderland University medical school and as an associate non-executive director for the University Hospital of North Midlands, a large acute hospital trust in Stoke-on-Trent.