Professor Knowles is Director of the NIHR Enteric Healthcare Technology Cooperative, Director of the National Bowel Research Centre and Surgical Specialty Lead for North Thames NIHR CRN.

He holds research positions in the European Society of Coloproctology and Association of Coloproctology of Great Britain and Ireland. He is Chair to UEG-led international working groups in anorectal physiology and GI neuromuscular diseases.

He serves as a member of the Rome IV committee for anorectal disorders and is on the global expert panel for Medtronic. He is a panel member for NIHR i4i and is on the editorial board of two journals. He has authored over 150 peer-reviewed publications as well as contributing several book chapters to major colorectal and general surgical texts.

He is also a trustee of Bowel & Cancer Research.