If tests show that the controversial amulet found on a Romano-British site at Shepton Mallet does not date from the fourth century AD local historian Fred Davis has another theory – which makes it a relic from the grave of a Saxon martyr.

The silver-alloy amulet was found in a grave during a dig in 1990. The Chi Rho symbol pricked into its surface was a well-known Christian device, and the suggested date of the tomb made the object the earliest positive proof of a Christian burial in England.

But when it was examined by the British Museum shortly after its discovery the silver in the metal cast doubt over a Roman dating.

Somerset County Museum Service has now arranged further sophisticated tests and the results will be announced tomorrow.

Peter Leech, the Birmingham University archaeologist who was in charge of excavations at the time, said the amulet was found in an undisturbed grave, so it was not fake.

Mr Davis, a local historian who was at the excavations when the amulet was found, believes the cemetery may have been the last resting place for a party of Irish pilgrims.

The group included St Indractus, and his sister, Drusa, who were murdered by some of Wessex King Ina's men as they journeyed home to Ireland via Glastonbury Abbey in the early eighth century.