Want to solve GCHQ's Christmas puzzle? Team up

British surveillance agency advises cryptography enthusiasts to join forces if they want to meet Sunday deadline

The British surveillance agency GCHQ has hinted that cryptography enthusiasts determined to complete its complex Christmas puzzle before Sunday's deadline should work in groups to make it through the five stages of the test.

The authors of the fiendish test, which has so far not been completed by anyone, also said entrants were getting too excited about the rumoured prize; the winner would receive "a signed book and some token GCHQ keepsake - maybe a paperweight".