A Question of Attribution 1991 one on netflix

Sir Anthony Blunt, who was a Soviet agent for 25 years, is routinely questioned and gives no answers, but is knighted and works as Director of the Courtauld Institute, and presents his interrogator with a puzzle in the shape of a doubtful Titian painting. He also does art restoration work in Buckingham Palace, where he gets into an interesting conversation with HMQ.