The coded series of hand-written letters on a cigarette paper-sized sheet – headed “Pigeon Service” – were discovered in a small red canister attached to the bird’s skeleton found up a chimney at a house in Bletchingley, Surrey.
David Martin, 74, a retired probation officer, was renovating his 17th-century home when he found the remains of the dead “secret agent” carrier pigeon, which is believed to have got stuck in the chimney on its return from a top-secret mission to Nazi Germany.
Experts from the intelligence agency GCHQ said the message, which has 27 five-letter code groups, is impossible to crack without its codebook. They have appealed to retired spies and the public for help.
They were also left baffled by missing details, such as the date of the message and the identities of the sender, “Sjt W Stot”, and the recipient, “X02”.
However, it is known that the bird was named 40TW194 from the aluminium ring found on its leg (the first two numerals indicating the pigeon’s year of birth).
Experts assume agent 40TW194 was destined for the Bletchley Park, where codebreakers worked around the clock to crack the Nazis’ “unbreakable” Enigma code.
A GCHQ spokesman said: “During the war, the methods used to encode messages naturally needed to be as secure as possible, and various methods were used.
“The senders would often have specialist codebooks in which each code group of four or five letters had a meaning relevant to a specific operation, allowing much information to be sent in a short message. For added security, the code groups could then themselves be encrypted.
“Although it is disappointing that we cannot yet read the message brought back by a brave carrier pigeon, it is a tribute to the skills of the wartime code-makers that, despite working under severe pressure, they devised a code that was indecipherable both then and now.”
Mr Martin said he had previously shown the message to the late spy and intelligence officer Wilfred Dunderdale, said to have been the inspiration for Ian Fleming’s James Bond.
A specialist in counter- espionage, Mr Dunderdale lived near Mr Martin’s house after the war.
“When I showed him the bird and code, the blood drained from his face and he advised us to back off,” Mr Martin said. “He said nothing would ever be published.”
Colin Hill, curator of Bletchley Park’s Pigeons at War exhibition, said: “The message Mr Martin found must be highly top secret. We have more than 30 messages from Second World War carrier pigeons in our exhibition, but not one is in code. We know it’s an Allied forces pigeon because of the red capsule it was carrying, but that’s all we know.”
One theory is that an Allied spy or army unit sent the message by pigeon from France on 6 June 1944, during the D-Day invasions.
It is thought the bird might have attempted to rest on an open chimney due to exhaustion or become disorientated by bad weather before being overcome by fumes from a fire below.
Second World War homing pigeons played a vital role in the war effort. Because of the wartime radio black-out, homing pigeons were dropped behind enemy lines by RAF bombers and picked up by resistance fighters who attached secret messages to them before releasing them homeward.
The RAF trained 250,000 birds, forming the National Pigeon Service. Between 1943 and 1949, 32 were awarded the Dickin Medal, Britain’s highest possible decoration for valour given to animals.
Their wartime adventures hit the big screen in Walt Disney film Valiant, in which a woodland pigeon joins the Royal Homing Pigeon Service.