Police have detained three men who were acting suspiciously in Oxhey Avenue.
A member of the public telephoned the police about the incident at 12.30pm. When officers arrived the men ran off - prompting a chase involving patrol cars and a police helicopter.
The first man was detained at 12.40pm and the other two and 12.50pm.
A total of six police cars and a dog unit were used to detain the men. Officers are currently investigating whether an offence took place.