British police are investigating how an intruder breached the security of the Tower of London and stole a set of keys from the tourist attraction and home of the crown jewels.

Locks to the Tower's drawbridges and other rooms have been changed and "a staff disciplinary procedure is underway" after a man was caught trespassing in the early hours of November 6 and escorted from the premises, according to a royal palaces statement.

The stolen keys did not provide access to the Tower itself, Historic Royal Palaces said in a statement, but admitted a lapse in security.

"Our well-established security systems and procedures are robust. However on this occasion, these procedures were not carried out to the expected standard," it said.

The Tower was begun by William the Conqueror in the 1080s and has been used by British monarchs as a home, place of execution and a prison for traitors ever since. Henry VIII had Anne Boleyn executed here. The crown jewels on display at the palace include a solid gold crown weighing over 2 kilograms and the 105-carat Koh-i-Nur ("Mountain of Light") diamond.

A police spokesman said the incident was under investigation.

The Tower is traditionally staffed by ceremonial custodians, known as Yeoman Warders (nicknamed "Beefeaters"), former members of the British armed forces whose elaborate scarlet and gold tunics are one of the best-known symbols of the capital.

Reuters