Amateur archeologists digging up an ancient burial ground where victims of the black death were laid to rest may have found evidence of a 600-year-old monastery.

A total of 25 plague victims were dug up at the site in Charterhouse Square, Clerkenwell, last year during work for the Crossrail project, but experts believe there could be more skeletons in the mass grave.

The new dig is to uncover evidence of a Carthusian monastery built in the 1400s to pray for victims of the bubonic plague, which killed 100million as it swept across Europe, and 90 volunteers were picked to help the team.

Nick Elsdon, from Museum of London Archaeology who is managing the project, said: “What we have found here is a medieval surface.

“What we can’t tell is whether it’s a courtyard or just a path.

“There is a good chance the kitchens and grounds are somewhere nearby. Because the Carthusians were vegetarians the meat kitchens were outside the monastery.

“We know it’s somewhere in the square but unfortunately we don’t know where.”

Maps from the 1600s clearly show a building in the square, while a team from Keele University have used radar imagery to detect possible remains several feet below the current surface.

“We wanted to dig in slightly different position,” said Mr Eldson. “But Islington Council wouldn’t let us because of the protected trees in the square.

“There is a chance what was detected by the radar is just demolished rubble. It’s was always an option.”

Joanna Cronin, one of the volunteers, said: “Although everything we find is fairly low key, you can’t help but be amazed by the history. I always apply for things like this but never get picked so I can’t believe how lucky we are.

Fellow digger Mary-Anne Brouckaert said: “Every single thing we touch is from the 14th century, which makes you think

’wow’. My children always play in the square and are really interested - they keep asking lots of questions.

Debbie Guiness, who has just qualified to be a Clerkenwell and Islington history guide, said: “It’s such a fascinating part of the world and it’s great to be able to learn more about it.”

The dig is scheduled to end on Saturday.