Don't know about the source but here goes:::
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A suspected terrorist plot to bomb British cities was foiled by British spies, The Sun reported.
The RAF intercepted coded messages between pilots flying from Amsterdam to an unnamed Middle-Eastern country. The code, which referenced pop music, was then decoded by British spies at GCHQ, who believe the pilots were trying to smuggle in explosives or chemical weapons. The plotters used the emergency frequency to discuss their plans.
Attacks in London, Bath, Bristol and Ipswich were allegedly planned for last November after the Paris attacks.
A Ministry of Defense spokesman said the government would not comment on issues of national security.
GCHQ is a British intelligence and security organization responsible for providing signals intelligence and information assurance to the British government and armed forces.
http://www.clarionproject.org/news/british-spies-crack-pop-song-code-and-foil-terror-plot#