A secret World War Two message found on the leg of a dead pigeon (Bletchley Park Trust/PA Wire)

A secret World War Two message found on the leg of a dead pigeon has left 21st century codebreakers flummoxed.

The code, hand-written on a small sheet of paper headed "Pigeon Service", was found in a small red canister attached to the bird's skeleton up a chimney at a house in Bletchingley, Surrey.

Experts from UK intelligence agency GCHQ said the message, which has 27 five-letter code groups, is impossible to crack without its codebook.

They were also left stumped by missing details, such as the date of the message and the identities of the sender, "Sjt W Stot", and the recipient, "X02".

A spokesman said: "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."

PA