In 1987 he was appointed Director of Imaging and Head of Department. In 1990, he was elected as Chairman of the Medical Advisory Staff Committee. He became the first Medical Director of the Whittington Hospital NHS Trust in 1992, a post he held for 5 years. He had a special interest in vascular, interventional and GI radiology up to his semi-retirement from the NHS in late 2010.
Dr Timmis is also lead consultant radiologist at the Hospital of St. John & St. Elizabeth, and a consultant radiologist at The Wellington Hospital in London. He has been associated with 4ways since its foundation, as consultant radiology advisor, and was appointed as Medical Director of 4ways in September 2011.