A man was arrested here when he tried to intrude into the Buckingham Palace while carrying a knife, a media report said.
The man, 44, was found attempting to go into the palace through its north centre gate. He was stopped by police, who searched him and found a knife, reported Xinhua citing the BBC.
The man has been taken into custody "on suspicion of trespassing on a protected site and possession of an offensive weapon", the report said citing police source.
The queen was not in the palace at the time of the incident. Buckingham Palace refused to make further comments.
Security issues at Buckingham have been raised lately after two suspects were nabbed there in September for attempted burglary. It was believed to be one of the most serious intrusions into the royal residence since 1982, when the queen woke up in a morning and was taken aback to see a stranger in her room.