Police have launched an investigation after an intruder managed to break in and steal keys from the grounds of the Tower of London.
Officials from the famous London landmark admitted they have been forced to change some of their locks after a set of keys was stolen from a sentry box at the fortress site.
Tower chiefs insisted that the Crown Jewels were never at risk of being stolen but admitted security procedures "were not carried out to the expected standard".
The keys gave access to the Tower's drawbridges as well as conference rooms and a restaurant, according to the Historic Royal Palaces, which runs the site.
A Historic Royal Palaces spokeswoman said: "We can confirm that an incident took place in the Tower environs in the early hours of November 6 and that this is now a police matter, so we are unable to discuss details.
"We can however confirm that during this incident, keys for a restaurant and conference rooms were taken together with a key to an internal lock to the Tower drawbridges that is not accessible from the outside.
"It would not have been possible to gain access to the Tower with any of these keys. All the affected locks were immediately changed.
"We have carried out an internal investigation and have concluded that our well-established security systems and procedures are robust.
"However on this occasion, these procedures were not carried out to the expected standard. A staff disciplinary procedure is under way to address this issue."
The attempted break-in caused some speculation on Twitter as to the thief's identity.
The Tower of London is famously guarded by the Yeoman Warders, or Beefeaters.
A Scotland Yard spokesman said: "An allegation of theft has been made to police, which is being investigated by Tower Hamlets CID."