If you needed more evidence that the police guarding the Palace of Westminster aren't kidding around ponder the mangled tooth of London prankster Stinescrimes.

At 3.30pm on 8 June, the 17-year-old approached police guarding the black barricade at the Houses of Parliament directly opposite Westminster Abbey. He had a simple question for one of the officers: "What would happen if I sprayed you with a bit of Silly String?"

He soon found out. And it was caught on video.

As the youth began spraying, police grabbed him and forced him down onto the steel barricade, bashing his face in the process. "Ow! My tooth," he is heard saying in the video and appears to look at a broken bit of one of his two front teeth.

Police would not name the youth because he is under-age and @stinescrimes would not return a request for comment on the incident either. The Met confirmed that he was arrested, but he has not been charged. The officer in the video is heard saying the arrest is for public disorder.

A day earlier the teen pulled the same stunt on an officer in Leicester Square and was kicked out of the area for 24 hours after getting a citation for anti-social behaviour under the Crime and Police Act 2014.

"I don't know what's in that spray fella," the officer said as he twisted the youth's arm, later saying that it "could be pepper spray" for all he knew.

"Can you stop being so aggressive?" the youth begs the officer, but is told: "We're not here as objects," by a female officer at the scene.

The video has 140,000 views on YouTube after it was posted 12 June. This is not the first prank the youth has tried to play on police in Westminster. Another video posted by the teen on 10 March shows him asking a police officer holding an automatic rifle at the Houses of Parliament if he can shoot them with a toy Nerf gun. The video has 1,663,243 views.

"In the US, they'd shoot you," says one commenter on the video. Since an armed gunman shot and killed a Canadian Army officer and stormed the country's Parliament last October, police at prominent sites in the UK have been on high alert.

Soldiers with assault rifles were posted at the entrance to Horse Guards Parade in Whitehall and at Buckingham Palace. A string of lone-wolf terrorist attacks in the West over the past year have also put authorities on alert.

The teen has been posting videos of his pranks on his Facebook page since at least November 2013 and has become part of a group called TrollStation who stage stunts throughout London.

One of Trollstation's other video pranks posted on 1 May has 224,000 views and shows one of the group's members presenting police with a fake knife and then running away when police move in to grab him. Their most recent video posted on 18 May shows one of the group's members posing as a ceremonial guard and staging a fake fight with another member.

"You think it's really funny to do that shit to police?" the female officer asks the teen in his most recent video. "It's crazy, man," he said later has he showed the citation they gave him.