The activities of Britain's secret service, MI5, are naturally something of a mystery, but recent revelations have renewed the debate about who controls the cloak and dagger brigade.
Details have emerged of British citizens who worked as spies for East European nations during the Cold War, but most concern comes from the suggestion that when the foreign agents were discovered, MI5 decided to keep details secret from its political masters. The source of the scandal comes from documents smuggled out of Moscow following the defection of a former KGB colonel.
Vasili Mitrokhin, 77, lives in Britain under an assumed identity in a concealed location after being given asylum as reward for his information on spies who worked for the Soviet Bloc.
Colonel Mitrokhin worked in the KGB's foreign office archives from 1956 until he retired in 1984, during which time he hand-copied thousands of documents about Soviet agents recruited overseas.
When the Soviet Union collapsed in 1992 he decided to defect and presented himself to the CIA. But after the US became suspicious of his overtures he offered himself to the British, who eagerly accepted him.
Mindful of the need to enhance his pension the defector struck a deal with MI5 that after they had examined his notes he should be allowed to offer them for publication. A lucrative deal was struck, linked to newspaper and television contracts, and the past two weeks have seen news bulletins crammed with details from his archives including the names of British agents alleged to have worked for the Soviets.
The first to be revealed was an 87-year-old great grandmother who used her position as secretary at a metals research agency to pass details of Britain's nuclear weapons programme to the Soviets. But further alleged agents include two former Labour ministers and a handful of academics.
Most of those named that have been tracked down by the press have openly admitted they had been happy to betray their country. But to the government's embarrassment it has since emerged that when these agents' activities became known to MI5 the agency decided not to prosecute them without telling the relevant cabinet minister of its decision.
Home Secretary Jack Straw is responsible to Parliament for the performance of the secret service and is ultimately answerable for any spy scandals. Last week he showed he was angry with MI5 for deciding not to tell ministers and ordered tighter control.
The agency claimed its decision was based on the fact that Colonel Mitrokhin's evidence was unlikely to have stood up in court, and referred to cases which were only of historical interest.
Such is the secrecy surrounding M15 that the government only admitted it existed in 1989. It was established more than 90 years ago as Military Intelligence section Five, with responsibility for counter-espionage in both World Wars before focusing on spies working for the Soviet bloc.
But the lack of oversight by governments has led to allegations MI5 was pursing its own political agenda, and was believed to have plotted to overthrow prime minister Harold Wilson's Labour government in the 1960s.
In an attempt to address its poor public image MI5 set up a Web site which includes a section on myths and misconceptions. 'The service does not kill people or arrange their assassination. It is subject to the rule of law in just the same way as other public bodies,' it says.
But despite these reassurances there continues to be a deal of public mistrust towards a body whose director general Stephen Lander, was recently listed as one of the most powerful men in the country yet has no public profile or accountability.