The Oxford laboratory that declared the Turin Shroud to be a medieval fake 20 years ago is investigating claims that its findings were wrong.
The head of the world-renowned laboratory has admitted that carbon dating tests it carried out on Christendom's most famous relic may be inaccurate.
Professor Christopher Ramsey, the director of the Oxford University Radiocarbon Accelerator Unit, said he was treating seriously a new theory suggesting that contamination had skewed the results.
Though he stressed that he would be surprised if the supposedly definitive 1988 tests were shown to be far out - especially "a thousand years wrong" - he insisted that he was keeping an open mind.
The development will re-ignite speculation about the four-metre linen sheet, which many believe bears the miraculous image of the crucified Christ.
The original carbon dating was carried out on a sample by researchers working separately in laboratories in Zurich and Arizona as well as Oxford.
To the dismay of Christians, the researchers concluded that the shroud was created between 1260 and 1390, and was therefore likely to be a forgery devised in the Middle Ages.
Even Anastasio Alberto Ballestrero, the then Cardinal of Turin, conceded that the relic was probably a hoax.
There have been numerous theories purporting to explain how the tests could have produced false results, but so far they have all been rejected by the scientific establishment.
Many people remain convinced that the shroud is genuine.
Prof Ramsey, an expert in the use of carbon dating in archeological research, is conducting fresh experiments that could explain how a genuinely old linen could produce "younger" dates.
The results, which are due next month, will form part of a documentary on the Turin Shroud that is being broadcast on BBC 2 on Easter Saturday.
David Rolfe, the director of the documentary, said it was hugely significant that Prof Ramsey had thought it necessary to carry out further tests that could challenge the original dating.
He said that previous hypotheses, put forward to explain how the cloth could be older than the 1988 results suggested, had been "rejected out of hand".
"The main reason is that the contamination levels on the cloth that would have been needed to distort the results would have to be equivalent to the actual sample itself," he said.
"But this new theory only requires two per cent contamination to skew the results by 1,500 years. Moreover, it springs from published data about the behaviour of carbon-14 in the atmosphere which was unknown when the original tests were carried out 20 years ago."
Mr Rolfe added that the documentary, presented by Rageh Omaar, the former BBC correspondent, would also contain new archeological and historical evidence supporting claims that the shroud was a genuine burial cloth.
The film will focus on two other recorded relics, the Shroud of Constantinople, which is said to have been stolen by Crusaders in 1204, and the Shroud of Jerusalem that wrapped Jesus's body and which, according to John's Gospel, had such a profound effect when it was discovered.
According to Mr Rolfe, the documentary will produce convincing evidence that these are one and the same as the Shroud of Turin, adding credence to the belief that it dates back to Christ's death.
