An inquiry is under way after a person broke into the Tower of London and stole a set of keys.
The incident took place in the early hours of 6 November and the intruder got past the first gate, a spokeswoman for the Historic Royal Palaces said.
Keys for a restaurant, conference rooms and an internal lock to the drawbridges were on the stolen set. The locks have now been changed.
Security was not up to "the expected standards", the spokeswoman said.
The Tower, which houses the Crown Jewels, is guarded by the Yeoman Warders or Beefeaters.
The Crown Jewels were not at risk and "at no point was the security of the Tower at risk", the spokeswoman added.
The spokeswoman for the Historic Royal Palaces said the intruder was found on site by security guards, but refused to reveal further details.
The Metropolitan Police said no arrests had been made as yet.
The Historic Royal Palaces spokeswoman added: "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 affected locks were immediately changed."
The spokeswoman said an internal investigation found that "our well-established security systems and procedures are robust".
"However on this occasion, these procedures were not carried out to the expected standard," she said.
"A staff disciplinary procedure is under way to address this issue."
The Metropolitan Police said: "We have received an allegation of theft and this is being investigated by Tower Hamlets CID."