A man carrying a "large knife" was arrested outside Westminster Cathedral in central London on Wednesday, police said.
Officers patrolling the area adjacent to the Houses of Parliament spotted the man "acting suspiciously" in an "area known for anti-social behaviour", Scotland Yard said in a statement.
The man "was found in possession of a large knife", and officers then placed him under arrest.
Scotland Yard said the incident was not terror related.
A Metropolitan Police spokesman said: “officers on routine patrol in the Victoria Street area of Westminster attempted to speak with a man who was seen acting suspiciously in an area known for anti-social behaviour.
“The man was found in possession of a large knife. He was arrested and taken to a central London police station where he remains in custody.”
“Enquiries continue,” the statement added.
The police officers were working as part of Operation Bobcat, in which plain-clothes policemen combat robbery and knife crime in Westminster.
