What is it? Click here for clues. (The immmediate impulse is to dismiss it as a hoax on the part of the Telegraph - bear in mind that bomb hoaxes are punishable by law in the UK.)

For hair-raising insights, see: Operation Blackjack Decoded. One of the most interesting and creative interpretations, IMhO, is OPERATION BLACKJACK — Terror Code 6/22/09 — By Captain Eric H. May, attempting to explain numerical codes buried in the press as a covert means of communication.