A warning from the spies at GCHQ: a robber is on the loose, intent on stealing Christmas presents. Luckily, he won’t find it easy.

The robber’s target, according to the British intelligence and security agency, is a house with a large number of rooms, each of which has a letter, which are linked to each other by coloured doors and arrows. He can’t go through the same-coloured door twice in a row, and can’t move against any arrows. Eventually, the robber is caught by the police. How was he acting?

The answer to this question – and six other festive brainteasers – can be deduced from the spy agency’s annual Christmas card, which for the first time this year features designs by schoolchildren alongside its famous puzzles.

Seven knotty questions have been set by GCHQ’s in-house puzzlers,

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