The Cambridge Five spy ring were constantly drunk, according to their Russian handlers, and regarded as incapable of keeping secrets.
Donald Duart Maclean and Guy Burgess, two of the five Cambridge University students recruited to spy for Russia in the 1930s, are described in the Russian documents.
Burgess was "constantly under the influence of alcohol", it says, going on to describe how he had once managed to drop a file of documents taken from the Foreign Office on the pavement outside a pub.
Four members of the 'Cambridge Five' - clockwise from top left, Anthony Blunt, Donald Duart Maclean, Kim Philby and Guy Burgess
Maclean was "not very good at keeping secrets", the file continued, also describing him as "constantly drunk". He had told his brother and a lover that he was a Soviet agent whilst drunk, the file said.
The Soviet reports on the five are revealed for the first time as the Mitrokhin Archive, the papers smuggled out of the KGB by Major Vasili Mitrokhin in 1992, become available to the public.
The archives contain profiles of all the Brits who worked as spies for the Russians. According to the files, which have been held in a secret location for more than 20 years, Burgess handed over 389 secret documents in just six months to the Russian spy agency, the KGB.
The pair, along with Kim Philby, Anthony Blunt and a fifth man, alleged to be John Cairncross, attended Trinity College, and passed information to the Russians for around two decades.
Burgess, who previously worked for the BBC, eventually became an assistant to Foreign Office minister Hector McNeil, and secreted out documents, photographed them, and returned them the next morning. Maclean also worked at the Foreign Office, in embassies in Paris, Washington and Cairo. In 1951, Burgess and Maclean fled to Moscow. Maclean learnt Russian, became a colonel in the KGB, and adapted well to life in the Soviet Union, but Burgess spent most of the rest of his life in a sanitorium on the Black Sea
Philby was head of MI6's anti-Soviet division - all the while operating as a KGB agent.
Mitrokhin had always made it clear after his defection that he hoped the files would eventually be available to the public. Now 19 out of the 33 files, all in Russian, can be viewed at the Churchill Archive Centre in Cambridge.