Today its very existence could be regarded as a mystery, stranded lonely on a pinnacle amid fields of corn and overlooking marshland.

However, the unearthing of an ancient stone coffin could soon shed important light on a time when St Mary's Church, Fishley, near Acle, was at the heart of a wealthy estate where King John was said to come hunting along the shore of what was then a bay.

World leading church historian Dr Julian Litten will examine the lid of the early 13th century coffin - found under soil in the churchyard - in a special event to mark Open Churches Week.

The public is being invited to come along between 11am and 1pm on Friday next week to watch him carefully brush away earth to look for symbols on the lid that may give a clue to the identity of the person buried in the coffin beneath.

One theory, which could be confirmed by the presence of a distinctive type of cross, is that it might be the burial place of an early priest; another is that it might be the coffin of a nobleman.

The site investigation by Dr Litten, of King's Lynn, who oversaw the burial of the unknown mariner from the Tudor ship Mary Rose at Portsmouth Cathedral in 1984, will be the culmination of years of detective work by church warden Ivan Barnard.

The trail for the retired MoD technician started 21 years ago when a much smaller stone coffin lid was found in long grass by the tower and subsequently put on display inside the church.

Combing through parish records, Mr Barnard, 68, of Fishley View, Acle, discovered the coffin was one of possibly three which had been moved out of the church during structural renovations undertaken in the 1860s by then estate owner Sophia Edwards.

However, it was not until last August that he found a second coffin - twice the size of the first - under 150 years of accumulated soil and dust in the churchyard.

He said: 'I had noticed a particular spot where the grass died back completely in hot weather. When I tapped it with a stick I found the stone coffin lid.'

Mr Barnard has sent Dr Litten preliminary photographs of the coffin lid - believed to be crafted out of Purbeck marble - so he can compare it to other finds around the UK.

He said: 'My own hope is that it could be a nobleman. King John, who ruled from 1199 to 1216, gave the tenancy of Fishley to his falconer who would keep goshawks for when he came to hunt.

'The coffins could be for the falconer and members of his family; the smaller coffin could be for a child.'

Mr Barnard said that depending on the findings of Dr Litten, they might consider seeking sponsorship for the examination of the coffin itself, a costly and complicated procedure requiring legal permission from the church authorities.

He said: 'We are also considering calling in another leading expert, Marianna Lines, who has developed a technique, using a cloth, to reveal details on stone which have disappeared through erosion.'

Findings from the investigation will be put on display in the church and also be sent to Norfolk Landscape Archaeology at Gressenhall.

Visit www.stmarys-fishley.com for information on the church.