Cold War spy Klaus Fuchs was told to throw a magazine into a London garden to set up a rendezvous with his Russian contact, a slice of everyday espionage life revealed by one of Britain's top intelligence officers in diaries that were released on Friday.

Fuchs, a nuclear physicist who was one of the Soviet Union's most valuable spies before being jailed in 1950, had to mark page 10 of the magazine to show he wanted to meet his contact, who would answer with a chalk-mark on a local lamppost.

The 10 diaries by Guy Liddell, then deputy director-general of the MI5 domestic spy agency, offer an insider's perspective at the dawning of a political system that would dominate the world for decades to come.

Liddell tirelessly documented his dealings between 1945 and 1953 with the UK government and other intelligence officials, including the government of Clement Attlee, and the "Cambridge Five" double agents whom Liddell mentions with affection.

Experts said the new diaries, which pick up where Liddell's previously released World War II diaries left off, contribute to the understanding of the period because they come from an authoritative source with a sharp mind and high-level access to classified information.

"We're getting a picture of what was going on at the center of the intelligence world, very much as it happened, from a person at the top, writing with complete candor, and someone who knew a lot of the individuals involved," said Andrew Lownie, a journalist and author on the intelligence world.

"We've got the whole beginning of the Cold War."

The diaries also offer details of what was happening inside the intelligence agencies when Donald Maclean and Guy Burgess, two of the "Cambridge Five" double agents who passed secrets to Moscow, fled the United Kingdom.

"It seems pretty clear that the pair of them have gone off," Liddell writes wryly in May 1951.

A few weeks later, he is still grappling with the new reality. "It seemed to me unlikely that a man of Burgess's intelligence could imagine that he had any future in Russia."

In one previously unknown case, another "Cambridge Five" agent Kim Philby, who in 1950 was stationed in Washington for MI6 while also passing information to the Soviet Union, sought to persuade Liddell to appoint him MI5 representative as well.

"I certainly gave him no encouragement," Liddell wrote.

Bond of secrecy

Liddell described how the discovery that the Russians had tested the atomic bomb in 1949 was announced to the Joint Intelligence Committee by William Hayter, then-chairman of the Foreign Office, under a "melodramatic bond of secrecy".

"Hayter cleared the room of secretaries and then said that if there was anybody present who could not keep what was going to be said to himself, would he kindly leave the room," he records in September 1949.

The discovery had "thrown everyone's calculations out of date", he wrote on New Year's Day in 1950, saying it was unclear if this was still an experimental bomb.

"It is, however, clear, that by 1957, at any rate, the Russians should have sufficient atomic bombs to blot this country out entirely."

Some experts believe the Russians were able to develop atomic weapons at least one year ahead of schedule because of the information passed to them by Fuchs.

The Fuchs scandal strained relations with the United States, which was furious that the leakage had taken place.

In 1950, an exasperated Liddell writes that the Americans "are utterly incapable ... of seeing anybody's point of view except their own. And that they are quite ready to cut off their noses to spite their faces!"