Met Police says a man has been arrested for possession of weapons near the Houses of Parliament after incident near Downing Street.
Eyewitnesses say a man was tackled by several armed policemen and handcuffed and that there are 2 knives on the ground.
Buildings near the Treasury were placed on lockdown during the scare on Thursday.
One man was arrested and nobody was injured, Scotland Yard said.
Armed police were spotted descending outside the government offices as police cars blocked the road on Parliament Street.