When Mr Paddy Scott developed agonising stomach pains in 2017, the possibility of cancer never entered his head. The British expedition photographer and film-maker, whose work often took him into rugged or dangerous terrain, was just 34 years old and prided himself on his physical fitness.

After his general practitioner (GP) referred him to hospital for a colonoscopy, the clinician who administered it asked if he would take part in a trial of a new blood test designed to detect tumours. The invitation struck Mr Scott as strange.