I suffer from white-coat syndrome. I am a squeamish man; just typing words like ‘scalpel’ or ‘catheter’ makes me queasy. I nearly fainted spellchecking ‘haemorrhage’. So it’s ironic that I’ve had to play so many medicos.

Nigel Havers quickly cottoned on to my weakness when we played doctors in the 1980s sitcom Don’t Wait Up. Our surgery was stuffed with medical textbooks and before a scene in front of the studio audience, he’d find a particularly gruesome image of a gangrenous leg or weeping ulcer and flip it open as I was about to speak, then gleefully watch me turn to jelly.

Once, in Casualty, I had to perform open-heart surgery. I knew the ribcage, heart and all the gubbins inside were made...