If you're growing up in a chaotic world without reason, your instinct is to become a performer and control the circumstances around you. You lead from weakness into strength; you have an undefended back.

When I was 16 or 17, anyone could have had me if they sang the right song and recruited me in the right way. Which is why I've always had a sneaking understanding for people who took the wrong route. That doesn't mean to say I took it or even contemplated it myself.

I wrote 'The Spy Who Came in from the Cold' at the age of 30 under intense, unshared personal stress and in extreme privacy. As an intelligence officer in the guise of a junior diplomat at the British Embassy in Bonn, I was a secret to my colleagues, and much of the time to myself.

I've had nothing to do with the intelligence world since I left it, in any shade or variety.