It's the stuff of spy novels, except in this case it's the stuff of actual spycraft. A new exhibit opening in London features ...

A passport belonging to one of the Cambridge spies, a 110-year-old lemon used for invisible ink and a letter about the Queen's response to news of a Soviet agent in Buckingham Palace are among MI5 ...

A 110-year-old lemon used by a German WW1 spy to send secret messages from Britain with invisible ink is going on display in MI5’s first ever public exhibition. The blackened and flattened fruit ...