Heron Tower and the surrounding areas near Liverpool Street were put into lockdown as a man dubbed the "French Spiderman" scaled the building earlier today (October 25).
Shocked and bemused onlookers were told to leave the area as emergency services cleared the area in central London.
Dan Marks, who filmed the footage, was on his way back from a meeting near the Gherkin when he realised there was a lot of commotion around the Heron Building.
Marks said: "Squinting in the rough direction of everyone's stares I caught sight of a tiny figure of white and black climbing the outside of the nearby building. "
He later added: "The crowd were generally good-natured and finding jokes to make, as Londoners always do when confronted with anything out of the ordinary."
