Fascination with the Holy Grail has lasted for centuries, and now the Bletchley Park code-breakers have joined the hunt. But what is it that's made the grail the definition of something humans are always searching for but never actually finding?

Could an obscure inscription on a 250-year-old monument in a Staffordshire garden point the way to the Holy Grail - the jewelled chalice reportedly used by Jesus and his disciples at the Last Supper?

That is one theory entertained by Richard Kemp, the general manager of Lord Lichfield's Shugborough estate in Staffs.

Kemp has called in world-renowned code-breakers to try to decipher a cryptic message carved into the Shepherd's Monument on the Lichfield estate.

The monument, built around 1748, features an image of one of Nicholas Poussin's paintings, and beneath it the letters "D.O.U.O.S.V.A.V.V.M."

It has long been rumoured that these letters - which have baffled some of the greatest minds over the past 250 years, including Charles Darwin's and Josiah Wedgwood's - provide clues to the whereabouts of Christ's elusive cup.