Senior officers will have to explain to the Home Secretary how a man managed to scale a 12ft fence, evade dozens of armed police, apparently kick down a door and make his way into the state rooms, which are accessed through an inner courtyard of the Palace.
He was finally arrested when he set off a motion detector in the room.
The Queen was informed of the incident, which happened last Monday night, hours later, while she was on holiday at Balmoral.
