Terrorist attacks on four British cities were thwarted last week after two pilots were intercepted discussing the plan using their “mayday” channel.
The pilots were discovered after using the mayday channel, which they did not believe was monitored. The attacks would have hit Bath, Brighton, London and Ipswich.
According to a report by the Sunday Express, the two pilots, one of whom worked for an airline that is on an intelligence service watch list, were thought to also be preparing to smuggle in chemical weapons or explosive devices.
“Alarm bells rang after several communications in code involving overseas airline pilots were picked up by chance,” a senior RAF source told the Daily Express. “We can only assume that they considered it safer to use this frequency than other modes of communication.
“We immediately passed these to the security services who then asked us to monitor certain airlines entering U.K. airspace.”
The discovery is believed to have triggered Operation Templer, which saw 10,000 soldiers deployed to support the British police.
The location of the pilots is not known but their identities are. The pilots have also been placed on high-profile watchlists.