Today's arrest at Buckingham Palace follows a number of security alerts - last month a suspected burglar managed to get into the building after scaling a fence.
He was found at around 10.30pm on 2nd September in a room that had been open to the public during the day.
A second man was arrested outside the Palace on suspicion of conspiracy to commit burglary.
Less than 48 hours later, amid heightened security, two police officers confronted the Duke of York in the Palace gardens demanding to know who he was.
Scotland Yard issued a public apology to the Duke, which he later accepted.