“At the beginning of the Cold War, Cambridge was producing the best agents for both sides. MI5 did not do very well in tracking down the magnificent Cambridge Five, largely because the defector named Anatoly Golitsyn, who defected in the beginning of 1960s to the CIA, knew certain amount of real intelligence, but he added on fabrications [including on the Cambridge Five]”, he said.

“The KGB was huge. There were never any constraints ever on its growth in size, and the same is true of [Russia’s] intelligence services. MI5 is a tiny fraction of the size of the KGB, so the simplest method that the KGB could use for defeating MI5 was simply to flood London with KGB and military intelligence GRU officers, who could run more agents than MI5 could possibly track on,” revealed Andrew. “In the end, the British government in 1971 sent back to Russia 105 Soviet intelligence officers. No other country in the West, the US included, ever came close to that, but it turned Britain from being a soft target for Russian intelligence, which it had been up to 1971, to a very hard target. It remained that way to the end of the Cold War.”

Christopher Andrew admitted that in the 1960s some British MPs worked either for KGB or for Czechoslovak intelligence that was a part of the Soviet bloc, though they did not have significant influence in the Cabinet.

“If [Soviet defector] Oleg Penkovsky had not told the given information to the West on the part that Soviet missile bases were being constructed, the Americans would not have been able to tell at the time of the Cuban missile crisis whether or not the bases constructed there were operational. If they had seen that they were operational – we might not be sitting here having an interesting discussion,” he noted.

Christopher Andrew also mentioned that MI5 never tortured terror suspects because it is a big mistake, as a tortured man could say anything against himself.

During a seven year period Christopher Andrew has had an unprecedented, phenomenal and virtually unrestricted access to 400,000 files, many of which are multivolume, of MI5 archives. He has also recently published a book to mark the 100th anniversary of the agency founded in 1909 (five years ahead of the First World War) to deal with the chief security problems of Great Britain.