Sir Ken McCallum, MI5 director general, said the exhibition is part of its "ongoing commitment to being open wherever we can".
The initialled leather case, containing papers and photos, was left at London's Reform Club by escaping Soviet double agent Burgess, one of the Cambridge Five spy ring.
image [https://cdn.magzter.com/1583504377/1743552593/articles/51IbRZR0i1743571709985/3449137375.jpg]
Lemon
He fled with fellow agent Donald Maclean. None of the group stood trial for spying.
Another exhibit is an ancient lemon used by German spy Karl Muller to provide juice for his invisible ink messages about British troop movements. He was executed by firing squad at the Tower of London in 1915.
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