Pupils are being challenged to put their codebreaking skills to the test in a festive brainteaser set by the UK's intelligence agency GCHQ.

The puzzle features on a Christmas card sent by Sir Jeremy Fleming, director of the Cheltenham-based spy agency.

Secondary schools across the country are trying to crack the code, intended to test problem-solving skills.

"Puzzlers need to combine a mix of minds to solve the seemingly impossible," said Sir Jeremy.

The Christmas card features seven "fiendish" puzzles and is aimed at testing schoolchildren's knowledge of key subjects and their ability to work as a team.

"The puzzles are based on the seven disciplines of languages, engineering, codebreaking, analysis, maths, coding and cybersecurity - all key skills needed at GCHQ to help keep the country safe," a spokesman said.

But this year's challenge comes with an added twist, as once all the puzzles are solved, schoolchildren will then need to use the design on the front of the card to assemble the answers in order to form three locations.

Joining those place names together will reveal the final answer.

The intelligence agency said pupils would need to employ all their skills of lateral thinking, ingenuity and perseverance to be successful.

"From breaking Enigma to harnessing the latest cutting-edge technology, our brilliant people have worked together throughout our history to help keep the country safe," said Sir Jeremy.

"This year's GCHQ Christmas Card Challenge gives an insight into the skills we need every day as part of our mission," he added.

Schools interested in taking part can find a resource pack on the GCHQ website.