Bones found by contractors laying new gas mains could be almost 1,000 years old.
National Grid contractors made the macabre find as they were digging in the Saturday Market Place on Friday.
Today National Grid said the bones were believed to date from the 12th - 13th Century, while St Margaret's Church - now Lynn Minster - was being built.
The work was stopped whilst the police carried out the initial investigation. The bones, thought to be part of a pelvis, some finger bones and other bones not identified at the time have now been taken away to be examined.
A National Grid spokesman said: 'Although not an every day occurrence, we do occasionally find bones in the excavations we dig, whilst replacing gas pipes.
'Proper procedures were followed and the relevant authorities dealt with the situation quickly.
'Although only a rough guess, the bones were thought to be from the time of the church was built around the 1100s.'
King's Lynn historian Dr Paul Richards said: 'If you dig deeper I'm sure you would find more human skeletons there. It's no surprise to me that the bones were found.
'It would be interesting to see if the skeleton could be dated. That part of Lynn, around the church, could do with an archaeological dig. That was where the town started.
'Until about 1600 that side of the church was the cemetery, while the other side was a monastery, where the monks lived. The cemetery operated from about 1100 to 1600, so the bones must be before 1600. There was also a charnel house there. Skeletons would be dug up and housed in the charnel house. The churchyard had a wall around it, and Saturday Market Place would be squashed up against this wall.'
Canon Christopher Ivory, vicar of Lynn Minster, said that, unless more work needed to be carried out by archaeologists on the bones, they would be buried to the south side of the church in a few days. He said skeletons had previously been recovered from the burial ground. He added: 'It's not a complete skeleton but they are human bones.'
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