When I reached Purley station I realized that I had not brought Sir Karl Popper's address with me. I accosted the taxi-man facing the station and tried out the name on him. 'Is he a professor-type?' 'Yes.' And away we went to Welcomes road, in the bright white freezing sunlight. It seems that people arrive at Purley Station from all over the world to pay homage to the great man, now aged 91.

Although Sir Karl was born in Austria he became a British citizen in 1945. As professor of logic and scientific method at the London school of economics he became, both as teacher and writer, one the greatest influences on 20th-century political and philosophical thought.

Mrs Melita Mew, who runs Karl Popper's life, met me at the door. Our last call had been fraught with anxiety - she had asked me to cancel my visit because Popper had a pain following a telephone conversation with a philosopher friend. They had been discussing the laws of probability but the talk had moved swiftly on to the subject of crime on television. Popper had become furious and agitated at the dismissal of his view that crime on television had a direct influence on society. For two days he had neither eaten nor drunk.

A few days later Mrs Mew rang me to say he had refused to go to hospital and had recovered. She turned out to be a good looking woman of ...