THE Soviet Union used civil airliners to conduct secret Cold War spying missions over Britain.

Some aircraft switched off transponders, alerting air traffic controllers to their position before veering off their approved flight paths to carry out aerial intelligence-gathering missions over sensitive targets.

Defence Secretary John Nott told Margaret Thatcher in December 1981 the RAF was monitoring hundreds of monthly flights through UK airspace by Warsaw Pact airliners, papers released by the National Archives under the 30-year rule show.

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