The Tower of London was hit by a burglary when a thief reportedly stole the guards' keys on Bonfire Night.
According to The Sun, the raider scaled two huge gates and ransacked a metal box which was supposed to have been locked at a sentry post.
The thief was spotted but managed to escape as the guards were unable to leave their posts and were ignored when they radioed for help.
The heavy bunch of keys includes ones to unlock drawbridges, plus others to conference rooms and the restaurant.
Tower officials were forced to spend thousands of pounds urgently changing the locks and were said to be 'livid'.
The Sun reports that officials insisted after the Met launched a major hunt for the thief that the Crown Jewels were never at risk of being stolen. But they admitted security procedures 'were not carried out to the expected standard.'
A source told the newspaper: 'Security was a total shambles. The burglar climbed over the Front Gate then got over another gate and found a metal box with the keys inside.
'The box is supposed to be kept locked at all times but it was open.
'It went from bad to worse. Guards saw him but could not leave their positions to chase him. They tried to radio a night watchman but got no response.'
The fortress is famously guarded by the Yeoman Warders, or Beefeaters, who are backed up by a private security firm.
A spokesman for Historic Royal Palaces, which runs the iconic Tower notorious for housing prisoners to be beheaded, told The Sun: 'A staff disciplinary procedure is under way.'
This is not the first time a thief has entered the Tower of London. In 1671, a mallet-wielding Irishman stole the Crown Jewels after he smashed the keeper of the Jewel House, where they are kept, over the head.
Colonel Thomas Blood squashed down the State Crown of Charles II to hide it under his cloak. He was captured trying to flee but the King gave him a pardon.
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