Builders discovered the remains of several Archbishops of Canterbury from the 17th century beneath a medieval parish church in south-west London.
Workers renovating the deconsecrated church of St Mary-at-Lambeth found a hidden crypt containing 30 lead coffins.
Site manager Karl Patten said his team were lifting flagstones and exposing the ground in the church when they uncovered what looked like an entry to a tomb.
To search the void, located next to Lambeth Palace, they used a mobile phone camera as their guide.
In the hole they found the remains of five Archbishops of Canterbury that date back to the 1660s.
Garden Museum Director Christopher Woodward said he received a call from the builders and immediately assumed something went wrong with the project.
"But wow, it was the crown - it's the mitre of an archbishop, glowing in the dark,” he added.
The red and gold mitre was resting on top of one of the coffins - which were stacked on top of each other in a brick-lined vault.
The parish church of St Mary-at-Lambeth was built opposite Westminster in the 11th century by the sister of Edward the Confessor.
It was the chosen burial place for various Archbishops of Canterbury from the 1660s.
The coffins contain the remains of Richard Bancroft, who oversaw the production of the King James Bible in 1611, as well as clergyman John Moore and his wife, Catherine Moore.
According to the church’s records, another three Archbishops are probably buried there.
Their names are Frederick Cornwallis, who was in office from 1768 to 1783, Matthew Hutton – 1757 to 1758 - and Thomas Tenison – 1695 to 1715.
A sixth Archbishop, Thomas Secker, who was in office from 1758 to 1768, had his internal organs buried in a canister in the churchyard.