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.

'The Spy Who Came in from the Cold' was the work of a wayward imagination brought to the end of its tether by political disgust and personal confusion.

The spy who came in from the cold.

The merit of 'The Spy Who Came in from the Cold,' then - or its offence, depending where you stood - was not that it was authentic, but that it was credible.

It's part of a writer's profession, as it's part of a spy's profession, to prey on the community to which he's attached, to take away information - often in secret - and to translate that into intelligence for his masters, whether it's his readership or his spy masters. And I think that both professions are perhaps rather lonely.

I began writing when I was still in the British Foreign Service, and it was then understood that even if you wrote about butterfly collecting, you used another name.