The latest figures, provided by the Cabinet Office, show a fall in the number of people employed by the Security Service, Secret Intelligence Service, and the Government Communications Headquarters (GCHQ), from 11,110 in 1992-93 to 8,448 this year.
The reduction follows the break-up of the Soviet empire, along with a decline in concern about the threat posed by subversion, accompanied by two cessations of IRA activity.
However, in a clear effort to justify its continuing existence, the Security Service, MI5, successfully lobbied ministers for agreement that it should be allowed to divert under-used resources to helping the police and Customs with the expanding threat from serious crime.
That role was embodied in statute by the Conservative government, with Labour approval, and it appears to have staunched the cuts in staff numbers.
The decline in the role of the services has been matched by two phenomena - a marked reduction in the number of security scandals, and the greater openness of the services themselves.
The 1960s, 70s and 80s are littered with reports on security lapses and scandals, including the cases of Vassall, Profumo, Lambton, Blunt, Prime and Bettaney - not to mention the allegations made by the former MI5 officer, Peter Wright, that Security Service personnel had conspired against Harold Wilson when he was prime minister.
Staff cuts have also been matched by a cutback in overtime, down 38 per cent since 1992; perhaps the most significant indication of reduced activity.
The most curious element of the current year's treasury supply estimate for the Security and Intelligence Services, is an estimated capital budget of pounds 144,535,000.
Given that both MI5 and MI6 have in recent years obtained prime-site headquarters buildings overlooking the Thames, at Lambeth and Vauxhall bridges, it is not clear what "works and equipment" could be costing so much, unless GCHQ's eavesdropping requires new satellites.
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