Oleg Gordievsky, who has died aged 86, was a colonel in the KGB who served as an agent for MI6, the Secret Intelligence Service, from 1974 to 1985, when he defected to Britain; his reporting was important not only in intelligence terms, but also as a significant political influence on East-West relations during the later stages of the Cold War. The fact that he was a good KGB officer made him a good MI6 spy – being gifted with a retentive memory, adept at sifting fact from opinion and always clear about what he did not know. Read full obituary.