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New lines of tapping

01 September 1994

The introduction of digital switching in the telephone system has changed the method of telephone-tapping by British Telecom (BT) which it provides on an agency basis to MI5, Customs, Special Branch, the National Criminal Intelligence Service, and police forces. Under the old "Tinkerbell" system tapping circuits had to be physically connected to targeted phone lines. Now "taps" can be simply set up using the software programs within the exchange switching system, moreover this can be done remotely without ever going near the telephone exchange building.

The "requesting agencies" increasingly have intercepted calls relayed directly to their headquarters where they can analyse and transcribe telephone calls. The BT bill for internal agencies is sent to the Home Office - an estimated £10 million for a reported annual volume of 35,000 taps.

PBXs (Private Branch eXchanges) used in factories and offices used to present a greater problem because of the need to monitor all calls to track down the user of one extension phone. Now software developments, introduced by Oftel the telecom regulatory body, allow a single extension to be tapped.

The ability to tap digital public exchanges and PBXs remotely enables GCHQ (Government Communications Headquarters) to monitor phone calls in Moscow or Baghdad. Similarly, intelligence agencies outside the UK can tap into a phone here.

In addition to monitoring international cables, telexes, and e-mail (which goes down the phone line courtesy of the "Postmaster", BT), GCHQ compiles a weekly "Travel Digest", derived from intercepted communications, of the intended movements abroad of individuals identified on an MI5-produced watch list.

New Statesman & Society All about eavesdropping Patrick Fitzgerald. 29.7.94 pp30-31.