Builders renovating the Garden Museum, housed at the deconsecrated church of St Mary-at-Lambeth, found a hidden crypt containing 30 lead coffins.

The building works included leveling the floor of the Chancel in order to make the area accessible for a new gallery.

To lower the floor level, the contractors were required to lift and re-lay ledgers which had been built into the chancel floor 1851, some of which weighted up to 1,500kg.

Their removal revealed a concrete block. This was lifted to reveal a flight of steps – and, if you lowered yourself to your belly, a glimpse of an Archbishop’s Mitre glittering in the dark. This was the discovery of a recorded vault below the Chancel for high status burials, including those of five Archbishops of Canterbury.

Site manager Karl Patten said: “We discovered numerous coffins - and one of them had a gold crown on top of it”.

The remains date back to the 1660s.

Mr Patten, from the building contractors Rooff, said his team were exposing the ground, lifting the flagstones in the church, when they uncovered an entry to what looked like a tomb.

They used a mobile phone camera on the end of a stick to search the void.

Garden Museum Director Christopher Woodward said he received a call from the builders and immediately assumed 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 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 coffins have been left undisturbed, though builders have installed a glass panel in the chancel floor above them for visitors to catch a glimpse.

Two of the coffins had nameplates - one for Richard Bancroft (in office from 1604 to 1610) and one for John Moore (1783 to 1805) whose wife, Catherine Moore, also had a coffin plate.

Bancroft was the chief overseer of the publication of a new English translation of the Bible - the King James Bible - which began in 1604 and was published in 1611.

According to Mr Mount, St Mary-at-Lambeth’s records have since revealed that a further three archbishops were probably buried in the vault: Frederick Cornwallis (in office 1768 to 1783), Matthew Hutton (1757 to 1758) and Thomas Tenison (1695 to 1715).

A sixth, Thomas Secker (1758 to 1768) had his internal organs buried in a canister in the churchyard.

Also identified from coffin plates was the Dean of Arches John Bettesworth (who lived from 1677 to 1751) - the judge who sits at the ecclesiastical court of the Archbishop of Canterbury.

Beyond that, Mr Woodward said: “We still don’t know who else is down there”.

However, further clues may lie in the history of the church.