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. Carbon dating tests carried out 20 years ago on the Shroud of Turin suggested that the relic was a forgeryProfessor 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.advertisementThere 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.