When the scruffy-looking KGB officer walked into the British embassy in Riga, the Latvian capital, one of his first demands – after being offered a cup of tea – was that his unique cache of files on Moscow's foreign intelligence operations he smuggled out of the Soviet Union must be published.

Twenty years later, Vasili Mitrokhin's wish is beginning to come true. the first batch of 2,000 closely typed pages of notes he made from the KGB archives is being opened to the public.

The documents, including more than a hundred pages devoted to KGB claims about its "agents, controllers and cultivations" in Britain during the cold war, have been made available, after vetting by Whitehall weeders, at the Churchill Archives Centre at Cambridge University.

They say that Melita Norwood, communist party member and secretary of a British research association working on nuclear reactor technology, was recruited in 1935 by a former correspondent for the Soviet news agency, TASS, named Rothstein.

Codenamed Hola, Norwood "passed on a lot of valuable materials for nuclear energy which he accessed by removing them from her boss's safe, photographing them and then placing them back", according to her KGB file. She was awarded the order of the Red Banner and, "for many years of excellent work", a lifetime pension of £20 a month.

An editor of the left-wing weekly, Tribune, codenamed Dan, is claimed during the 1960s, to have published articles "based on KGB propaganda" and was paid £200 as a reward. The files describe how Guy Burgess, of the notorious Cambridge Spy Ring, was "constantly under the influence of alcohol", yet managed to provide the KGB with 389 documents in the first half of 1945, and a further 168 in 1949. Donald Maclean, another member of the Cambridge ring, is also described as being "constantly drunk" and "not very good at keeping secrets", telling his lover and brother about his "work".

In 1992 Vasili Mitrokhin travelled to Riga with a sample of his documents. He went to the UK embassy after being put off by a long queue at the US embassy. Photograph: Family handout/PA

An appendix in the archives copied by Mitrokhin suggest that the KGB claimed it had contacts with 200 people in Britain.

Mitrokhin's files record in meticulous detail how the KGB in the 1970s spied on the sermons and meetings of the Polish cardinal Wojtyla, later Pope John Paul II. They include maps identifying the location of KGB booby traps and hidden arms caches in western Europe.

They claim that Philip Agee, the former CIA officer who publicly named a list of US agents, had used material offered to him by the KGB, and that Yuri Andropov, head of the KGB in the 1960s and 1970s, infiltrated Ramparts, the radical US magazine which consistently opposed the Vietnam war and also published Che Guevara's diaries. Andropov played a key role in crushing the Prague spring in 1968. Mitrokhin's documents include a long list of targets, mainly editors and student leaders, which 15 "experienced intelligence agents" were ordered by Andropov to pursue in an operation the KGB named Progress.

Mitrokhin's files were translated for journalists at the Churchill Archives Centre by Svetlana Lokhova, a colleague of Christopher Andrew, the Cambridge historian who pioneered the study of intelligence agencies and later appointed MI5's official historian.

The FBI described the Mitrokhin files as "the most complete and extensive intelligence ever received from any source". However, intelligence analysts and some Soviet defectors have warned that the KGB seriously exaggerated the significance and number of its contacts and operations to impress the Soviet leadership – and increase its budget.

With the help, behind the scenes, of MI5 and MI6, Norwood was exposed in a blaze of publicity in 1999 when Mitrokhin and Andrew published a book based on the files. However, after MI5 was stung by criticism over its handling of her case, it played down her significance, saying her "value as an atom spy to the scientists who constructed the Soviet bomb must have been, at most marginal". She died in 2005.

The late Dick Clements, editor of Tribune in the 1960s described the story of Dan, first appearing in the Sunday Times, as "complete nonsense" and that the Soviet official responsible for the claim might have made it simply to fiddle his expenses.

Mitrokhin copied the files between 1972 and 1984 when he supervised the transfer of the KGB's foreign intelligence archives from the Lubyanka to its new headquarters in Moscow. He smuggled out his notes, typed them up in his dacha, and hid them under the floorboards.

In 1992, he took the overnight train to Riga dressed as what was described a street pedlar, hiding a sample of his documents under old clothes and sausages. He went first to the US embassy but was put off by the long visa queue there.

He then went to the UK embassy where he was put in touch with a young member of the staff who asked him: "Would you like a cup of tea?", before getting in touch with MI6 who later exfiltrated him and his family. Mitrokhin died in Britain in 2004. Asked about what kind of man he was, Andrew described experiencing the former KGB's officer's feeling of relief – that of a someone who, in the Soviet Union, had not been able to confide in anybody but himself for as many as 30 years.