Bletchley Park tries to crack a 250-year mystery: Do 10 letters at stately home lead to Holy Grail?

After five years worrying away at the Nazis' Enigma cyphers, 85-year-old Oliver Lawn could have been forgiven an air of nonchalance yesterday as he approached a 10-letter code, etched on a stone amid rhododendrons in rural Staffordshire. But the frown on his face as he grubbed around in the undergrowth indicated that the puzzle presented no ordinary decoding challenge.

After five years worrying away at the Nazis' Enigma cyphers, 85-year-old Oliver Lawn could have been forgiven an air of nonchalance yesterday as he approached a 10-letter code, etched on a stone amid rhododendrons in rural Staffordshire. But the frown on his face as he grubbed around in the undergrowth indicated that the puzzle presented no ordinary decoding challenge.

Carved on the base of the Shepherd's Monument, a white marble arbor at Shugborough Hall, the letters are D.O.U.O. S.V.A.V.V.M. and they have been flummoxing some of the nation's finest minds since they were put there circa 1748. Charles Darwin is said to have had a stab at decoding them, so too the local bigwig Josiah Wedgwood - both to no avail.

The mystery surrounding the uneven row of letters is seasoned with some big rumours, the most dramatic being that they may actually point to the Holy Grail. So Shugborough - the ancestral home of Lord Lichfield - has now drafted in Bletchley Park and its Second World War code-breakers.

Mr Lawn has in turn enlisted the help of of his 81-year-old wife Sheila, whom he met at Bletchley during the war. He is a mathematician (he was studying the subject at Cambridge when he was summoned to help break the Enigma code) but she is a language specialist. Their initial musings indicated that a good track record on the television programme Countdown would not be enough to solve the puzzle, since the letters are only a part of the problem. They needed to be observed in relation to the relief above them - a depiction of a Nicholas Poussin painting sculpted in mirror reverse by the Dutch artist Scheemakers with a number of strange changes from the original. "The inscription is obviously a classical reference," said Mr Lawn. "It's either Latin or Greek and based on some historical happening. But the picture's a funny one. Why it's a mirror image is very strange."

The answer to that and other questions may lie in the Shugborough archive, which Mr Lawn and other Bletchley experts will now examine. It reveals how Thomas Anson, an admiral in the British Navy attracted to codes by his seafaring days, commissioned the Shepherd's Monument to adorn the estate he built.

But it is his wife who provides the trail towards the Holy Grail. She is believed to have had associations with the Knights Templar religious movement, which was founded in the 12th Century and had links to Jerusalem and to Rennes Cathedral. It was in the same cathedral that a parchment containing a coded message including the words "Poussin ... holds[s] the key" were once discovered.

More prosaic solutions have surfaced over the years, including the conclusion that the first and last letters ('D' and 'M'), which sit slightly beneath the other letters, are initials for the Latin Diis manibus- which was etched on Roman tombs to dedicate departing souls.

In 1987, the current Lord Lichfield's grandmother also had a stab at the puzzle, claiming that a clergyman she knew as a child told her a legend about a shepherdess, Alicia, including the line "Out of your own sweet vale, Alicia vanish vanity 'twixt Deity and Man" (OOYOSVAVVDM). The legend has never been traced and the solution all but dismissed as an invention (almost) to fit the letters.

For Bletchley Park, a venue now open daily to visitors, the new challenge is not unique. The director, Christine Large, declines to discuss suggestions that GCHQ, the Government's top-secret "listening post", uses its expertise but the centre does work with Southampton University on educational programmes to nurture code-breaking talent. "Though computers are used a lot more, people are reverting to classical methods for answers," she said.

Ms Large is keeping an open mind about whether the "Shugborough Enigma", as she describes it, may point to the Holy Grail. But on first sight, it certainly seems Oliver Lawn was wise to draw on his wife's language skills.

"It looks as if it is a language-based puzzle which was prevalent at the time when the monument was made," said Ms Large. "It was how people protected information they wanted kept secret from families. It looks as if it's probably going to need language expertise - maybe Greek and maybe forgotten languages - as well as mathematics and puzzles."

There were many questions for her experts to consider yesterday. Is there significance in how the sculpted shepherd points at something different in Poussin's original painting? Do the full points after each letter suggest they stand for something? Is the message a key to a message somewhere else?

And there is another consideration probably best not dwelt upon by the Lawns, just now. "Of course, it is possible that the letters may be meaningless," said Ms Large. "They may simply be etched there to frustrate the many future generations."

BRITAIN'S WARTIME CODE-BREAKERS

* A small team of scholars-turned-codebreakers arrived at Bletchley Park, right, in the summer of 1939 to try to crack Germany's Enigma codes. They travelled in the guise of 'Captain Ridley's shooting party'.

* The odds against the Enigma codes being cracked - as they eventually were - stood at 150 billion billion to 1.

* The 10,000 people who worked at Bletchley at its wartime peak were described by Winston Churchill as "the geese that laid the golden eggs and never cackled". But by 1946 the place was deserted.

* In 1991, the Bletchley Park Trust was formed to preserve the site for posterity. Bletchley is now a popular visitor attraction ( www.bletchleypark.org.uk).

* The famous Enigma machine was stolen in April 2000 and became the subject of ransom demands before being handed in to the BBC's Jeremy Paxman two years later.

* Huts 3 and 6 are to become an international centre for interpreting the intelligence-gathering process at Bletchley Park, including showing how the huts were significant to D-Day.

* Bletchley Park's D-Day 60th anniversary programme includes the launch of a roll of honour of people who worked there during the Second World War.