It is a tale of secret agents and surveillance that could have come straight out the BBC's classic spy drama Tinker, Tailor, Soldier, Spy.
But the difference is that genuine spies were involved and they were operating behind the scenes at Broadcasting House rather than on the small screen.
Confidential papers, obtained by The Sunday Telegraph, have revealed that the BBC allowed MI5 to investigate the backgrounds and political affiliations of -thousands of its employees, including newsreaders, reporters and continuity announcers.
The files, which shed light on the BBC's hitherto secret links with the Security Service, show that at one stage it was responsible for vetting 6,300 different BBC posts - almost a third of the total workforce.
They also confirm that the corporation held a list of "subversive organisations" and that evidence of certain kinds of political activity could be a bar to appointment or promotion.
The BBC's reliance on MI5 reached a peak in the late 1970s and early 1980s at exactly the same time as millions of viewers were tuning into the fictional adventures of George Smiley in Tinker, Tailor, Soldier, Spy and -Smiley's People.
David Dimbleby, John Humphrys and Anna Ford all began their careers with the broadcaster when the system was still in place.
The papers show that senior BBC figures covered up these links in the face of awkward questions from trade unions and the press. The documents refer to a "defensive strategy" based on "categorical denial". One file note, dated March 1 1985, states: "Keep head down and stonewall all questions."
The BBC, however, has always refused to be drawn on the extent of its collaboration with the secret services.
It is only now, after a request by this newspaper under the Freedom of Information Act, that it has finally been willing to release details of the vetting operation.
Another internal BBC document, dated 1983, confirms: "We supply personal details to the Security Service. If there is any adverse information known, we receive this information and also, where necessary, an assessment based upon the involvement of the individual. This is presented to us as advice; line management then make the decision as to action."
The documents do not name any of the individuals subjected to vetting, but it is possible that some of the BBC's biggest names were scrutinised.
Different posts were vetted for different reasons. Senior officials, including the director-general, and their support staff were checked because they had access to confidential government information in relation to their jobs. But thousands of employees were vetted because they were involved in live broadcasts and the BBC was worried about the possibility of on-air bias or disruption.
In 1983, 5,728 BBC jobs were subjected to this second kind of scrutiny known as "counter-subversion vetting".
The vetting system, which was phased out in the late 1980s, also applied to dozens of other employees, including television producers, directors, sound engineers, secretaries and researchers.
The details of freelance television and radio staff were also routinely passed on to the security services and even the posts of editor and deputy editor of Radio 4's Woman's Hour were subject to background checks by MI5. In many cases, the spouses of applicants were also subjected to scrutiny.
The BBC tried on several occasions to be more open about the system, but was blocked by the Security Service. A memo, dated March 7 1985, states: "Secrecy of the complete vetting operation is imposed upon us by the Security Service - it is not of our making."
For their part, the security services were increasingly concerned about the number of people being referred to them by the BBC. During the first four months of 1983, they were asked to investigate 619 different individuals.
In the early 1980s, the BBC had a list of "major subversive organisations", which included the Communist Party, the Socialist Workers' Party, the Workers' Revolutionary Party, Militant Tendency, the National Front and the British National Party.
In contrast, CND, which was very popular at the time, was not regarded as a "subversive organisation". Youthful attachments to extreme causes did not necessarily mean an automatic ban on employment.
The papers show that, in 1968, Sir Hugh Greene, the BBC's then director-general, and John Arkell, the head of administration, successfully evaded questions on the issue during an interview with a journalist.
A memo from Mr Arkell, dated March 1 1968, to another senior colleague states: "You might like to get a bit of credit for the BBC next time you talk to MI5 by telling them that I stuck resolutely to the brief which you prepared for me in spite of very pointed and penetrating questions.
"I still denied that we had any vetting procedures."
The BBC declined to -comment.
http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/07/02/nspy02.xml
http://www.bilderberg.org/sis.htm#BBC
