Two daredevils posed as tourists before leaping 215ft from a cathedral tower in a dangerous base jump.
The two men bought tickets for a guided tour of Ely Cathedral on Sunday, August 9, when they left their group and threw themselves from the West Tower.
They landed safely on the Palace Green, stuffed their parachutes into their backpacks and ran off.
Cathedral administrator Stephen Bourne said: “The next thing we knew they were over the edge of the tower with their parachutes and in the air.
“A lot of people come into the cathedral with backpacks - most people just have their lunch or camera in them - not a parachute.”
He added: “They were soon spotted by members of cathedral staff and members of the public but obviously it was too late by then.
“The only way we could prosecute them would be for trespass but the fact they bought the tickets to go up the West Tower means they didn’t really trespass.”
Mr Bourne later spoke to the men who said they were base jumping professionals and had been planning the stunt for around three years.
Ely Cathedral, where filming is due to start for Netflix series The Crown starring Matt Smith next week, is now tightening its security.
Mr Bourne said: “It might be that we have to start searching people before they go on our tower tours and taking measures to prevent anyone from jumping off of any part of the cathedral.
“I hope we don’t have to do anything too drastic like they had to do with the Empire State Building, but it might be that some areas should be glassed.”
Police said base jumping was not illegal but they advised against people putting themselves in danger.