A giant tortoise that has been dubbed the world's oldest living creature may actually be an imposter, living under an assumed identity, it has emerged.

It had been reported that Jonathan, a present-day resident of St Helena, was living on the remote British island when Napoleon was exiled there back in 1815.

His claim to record longevity was based on a Boer War photograph of a Seychelles tortoise said to have been in the Atlantic island territory since Napoleon's time.

Both are called Jonathan and it was assumed that the tortoise now living on the governor's lawn was the one in the photograph.

But a St Helenian businessman and amateur historian, Nick Thorpe, has said he strongly suspects the creature in the picture actually died 90 years ago.