GCHQ releases 'most difficult puzzle ever' in honour of Alan Turing

12 riddles linked to new 50 note featuring the codebreaker may take seven hours to crack

GCHQ has released its most difficult puzzle ever", a set of 12 riddles linked to design elements of the new 50 note featuring the mathematician and codebreaker Alan Turing.

The questions begin with a relatively straightforward crossword-style puzzle that starts by asking where GCHQ's predecessor agency, where Turing worked, was based during the second world war. A two-word answer, nine letters then four, is required.