A huge haul of records opened up for the first time, has revealed the characteristics of Britons who spied for the Soviet Union.
Documents from the Mitrokhin Archive - said by the FBI to be the most complete intelligence ever received from any source - describe members of the Cambridge Five spy ring, recruited while at university in the 1930s.
Guy Burgess, one of the five recruits, is described as "constantly under the influence of alcohol".
One note details how on his way out of a pub, he managed to drop one of the files of documents he had taken from the Foreign Office on the pavement.
Another of the five men, Donald Duart Maclean, is described as "not very good at keeping secrets".
Notes on him say he was "constantly drunk", binged on alcohol and even told one of his lovers and his brother about his work as a Soviet agent while he was the worse for wear.
Major Vasili Mitrokhin smuggled the information out of Soviet archives during 12 years working for the KGB before defecting to Britain in 1992.
Many of his notes can now be viewed at the Churchill Archive Centre in Cambridge.