The hidden tombs of five Archbishops of Canterbury dating back centuries have been found by builders at a museum in a deconsecrated church in south London.

Workers at the Garden Museum in Lambeth uncovered 30 lead coffins and a bishop's mitre in the site of the old medieval church of St Mary-at-Lambeth. The building is next to Lambeth Palace, the official residence of the Archbishop of Canterbury.

Site manager Karl Patten told the BBC: "We discovered numerous coffins – and one of them had a gold crown on top of it".

Garden Museum Director Christopher Woodward said he received a call from the builders and thought that something had gone wrong with the project.

"But wow, it was the crown – it's the mitre of an archbishop, glowing in the dark," he said.

The hidden chamber was discovered by accident after site managers were trying to level a floor. They lifted the flagstones and cut a six-inch hole in the building's foundations, coming upon a secret cavity.

They were able to film inside by using a mobile phone on a stick, which revealed a hidden stairway leading down to a brick-lined vault. It was here that a number of coffins, stacked on top of one another came to light, according to a Sunday Telegraph report.

The coffins will be on display and visitors can look at the tombs of the archbishops through a glazed panel in the floor from May 2017. The tombs need to be protected as although most lead sarcophagi contain dry remains, some bodies decompose into a viscous black liquid known as "coffin liquor", according to the Telegraph.

The bodies of the priests include Richard Bancroft, who was archbishop from 1604-10, the earliest discovered in the secret burial plot. Bancroft was the chief overseer of the publication of the King James Bible – which was published in 1611.

Wesley Kerr, chair of the Heritage Lottery Fund from 2007-2014, said: "This is really astonishing – this is one of the most incredible things I've seen… To know that possibly the person that commissioned the King James Bible is buried here is the most incredible discovery and greatly adds to the texture of this project."

Other archbishops were believed buried in the vault are Frederick Cornwallis (in office 1768-1783), Matthew Hutton (1757-1758) and Thomas Tenison (1695-1715).