 Later he read Politics, Philosophy and Economics at University College, Oxford University, achieving First Class Honours, before graduating with Honours in Medicine from the Royal Free Medical School.Marsh was until 2015 the senior consultant neurosurgeon at the Atkinson Morley Wing at St George's Hospital, south London, one of the country's largest specialist brain surgery units.He specialises in operating on the brain under local anaesthetic and was the subject of a major BBC documentary "Your Life in Their Hands" in 2004, which won the Royal Television Society Gold Medal.