Professor Allen-Mersh trained in surgery at Charing Cross and Royal London Hospitals, and completed fellowships in colorectal surgery at St Marks Hospital, London, and in cancer surgery at Memorial Sloan Kettering Cancer Centre, New York. He was appointed as an NHS Consultant Surgeon in 1986, and awarded the title of Professor in 1997. He has written over a hundred papers on colorectal topics - including cancer, haemorrhoids, pilonidal sinus, and incontinence. He has been an accredited Consultant at Bupa Cromwell Hospital for over 25 years. He specialises in fluctuation in bowel habit, anal bleeding and discomfort, haemorrhoids, pilonidal sinus.