Revealed: Attlee's ignorance of the Cambridge spies who defected

Three weeks after two of Britain's most notorious spies defected to Soviet Russia, the Prime Minister and his cabinet were more concerned about the moral fibre of the Foreign Office than any threat posed to national security.

Top-secret papers released on New Year's Day reveal the true extent of the ignorance and incompetence at the heart of the then government and the intelligence services during one of the most serious breaches of security in British history. The classified notes, innocuously entitled "Foreign Office officials", were written by the cabinet secretary, Sir Norman Brook, on 11 June 1951.

Three weeks earlier, Donald Maclean, head of the US department in the diplomatic service in London, and Guy Burgess, a diplomat formerly based in Washington, had quietly deserted their posts and left Britain for Russia.

But the cabinet notes show that the prime minister Clement Attlee and the foreign secretary Herbert Morrison appeared more concerned with Donald Maclean's drinking and an allegation of attempted rape.

Although Maclean and Burgess were being investigated by MI5, Morrison defends Maclean, saying: "He has done very well at the Foreign Office. All we know is they have disappeared. Maybe a security aspect but no evidence that there is. Can't say much today." Attlee says both men are "doubtful moral characters". He asks: "Aren't Foreign Office a bit easy over this?"

Sir Richard Rapier Stokes, the Lord Privy Seal, then says Maclean had already been recalled from the British embassy in Cairo because of his drinking and says there was "also [an allegation of] attempted rape."

Attlee demands: "What is the standard of conduct at the Foreign Service? Is it high enough?" The foreign secretary says: "We don't know, one way or the other, whether they may have been engaged in espionage."

That Britain's prime minister and foreign secretary should be so in the dark about the serious implications to national security is extraordinary. Historians say that, along with other key members of the Cambridge spy ring, principally Kim Philby and Anthony Blunt, Burgess and Maclean represented the most effective espionage operation against US and British interests in the 20th century.

One former diplomat called the cabinet notes "surprising". Sir Crispin Tickle, who joined the US department of the British Diplomatic Service in 1954 , three years after Burgess and Maclean had defected, said: "When they left, I would have thought it should have been clear that they were betraying their country. The allegation [of rape] is news to me; in fact I'm not sure anyone knew much about a lot of this."

Air Marshal Sir John Walker, former chief of defence intelligence, said it should have been obvious the two men's disappearance was at the least suspicious. "If two people with their background suddenly up sticks to go to live in Moscow it must suggest something is wrong. It was very difficult to get into Moscow at the time and people simply didn't have this kind of change of lifestyle."

Sir Crispin added: "Maclean was regarded as an adequate, although not remarkable, head of department. I am surprised this should be said in cabinet. When I joined, he was of course seen in a very different light. But even then I remember coming across his minutes of meetings."

Sir Crispin said he was also surprised that the secretary's notes had not been destroyed, as was the custom. The notes are part of the first tranche to be released by the National Archives under the terms of the Freedom of Information Act 2000.

In 1981 it was concluded that extended closure of the notebooks was "proper". It was agreed that consideration should only be given to allowing access to the earliest notebooks when they were 50 years old. But in 2004 the cabinet secretary, Sir Andrew Turnbull, and the Master of the Rolls, Lord Phillips of Worth Maltravers, recommended that they should be released in tranches in January 2006.

Burgess, Maclean, Philby and Blunt

Guy Burgess met Kim Philby, Donald Maclean and Anthony Blunt at Cambridge University in the 1930s when they became secret supporters of the Communist Party.

Burgess worked for the BBC until 1938 when he joined the Diplomatic Service as a propaganda expert. By 1951 he had gained a reputation as a flamboyant, alcoholic homosexual. His conduct and suspicions about him meant he was recalled when he became the first secretary at the British embassy in Washington. He died in 1963.

Donald Maclean was the son of the Liberal cabinet minister Sir Donald Maclean. After the Second World War he worked in London before holding a senior post in the British Embassy in Egypt. But he returned to London in 1950 after being accused of wild behaviour. He later became head of the American department of the Foreign Office. After defecting to Moscow in 1951 he became a Soviet citizen. He died in 1983.

Kim Philby was a double agent in the British Secret Intelligence Service (SIS), working for the KGB. He rose to be the SIS's liaison officer in Washington with the CIA and the FBI, before he fell under suspicion after the defections of Burgess and Maclean. In October 1950, Philby warned Burgess and Maclean that they were being investigated by MI5. He died in 1998 after also fleeing to Moscow.

Anthony Blunt was a distant relative of the Queen and later keeper of the Royal Family's pictures and drawings. During the Second World War he joined the Security Service MI5. He sometimes sat on the Joint Intelligence Committee and had access to reports from the SIS and MI5. In 1963 an American, Michael Straight, one of Blunt's recruiting failures, told MI5 about him. Blunt was offered immunity in return for information on the KGB. He died in 1983.