According to the Sunday Telegraph the builders stumbled across the tomb while working at the Garden Museum, which is found inside an old church next to Lambeth Palace - the Archbishop of Canterbury's residence.
They were converting part of the old church into an exhibition space and began evening a floor when they made an accidental hole in it.
Seeing a form of chamber inside the hole they attached a mobile phone to a stick, dropped it down, and realised an archbishop's crown and several lead coffins were there.
It's now transpired the tomb of 30 sarcophagi contains five former Archbishops of Canterbury as well as a senior judge in the Church of England's Ecclesiastic Court and the wife of a former archbishop.
Identification of all 30 coffins is ongoing but those who've been verified lived in the 1600s and 1700s.
A video from the Garden Museum exploring the discovery in more detail is below:
