A set of keys is missing from a sentry box at the Tower of London. Police are investigating.
Consequently, some locks at the fortress have been changed since an incident on 6 November.
The keys were to the drawbridges as well as conference rooms and a restaurant, according to the Historic Royal Palaces, which runs the site.
A spokeswoman for the agency said it would not have been possible to gain access to the Tower with any of the (missing) keys. All the affected locks were immediately changed.
The Crown Jewels were never at risk of being stolen.
The Tower of London is guarded by the Beefeaters, Yeoman Warders.