This is the shocking moment a gang of youths steal a locked bicycle using an angle grinder in broad daylight outside a primary school before threatening onlookers who try to intervene.

The four masked thugs can be seen cutting through the Brompton-style bicycle chained up to railings in full view of numerous passers-by.

One of the gang jumps up on to the red bike, which sell for up to £1,200, to help break it free as sparks fly from the heavy-duty machinery.

A member of the public tells the gang: “Boys, I’m calling the police. You better go, run. F*** off. What are you doing? F*** off.”

As the thief pulls the bike loose, two members of the public half-heartedly holds on to the handlebars to stop them getting away, prompting the youth to shout: “Let go my bike. Let go my bike.”

His friend hands the boy the angle-grinder before the youngster raises it above his head and lunges towards the men, shouting: “F****** come near me, I dare you. Who’s gonna come near me?” - forcing the onlookers to drop the bike and retreat.

The gang then cycle off.

The incident took place outside London Fields Primary School and footage was posted online by Bethnal Green coffee shop Jonestown Coffee.

It said alongside the clip: “This video was taken by a customer of ours about 2wks ago. Location is near London Fields.”

It has prompted a slew of comments, with many suggesting the onlookers should have intervened more forcefully to stop the theft, and criticising the brazen nature of the incident.

Liam King wrote: “Im more shocked at all the people watching, allowing it to happen. London really has fallen,” with one user replying: “I’m not risking being stabbed for a push bike [...] insurance will cover that.”

Peter Stuart added: “I’m no judicial expert, but I’d say if he’d just stolen the bike he would have gotten away with it.

“Swing at someone with an angle-grinder in broad daylight, and chances are the police will take an interest, and the courts are going to take a very very dim view.”

Scotland Yard said an investigation was under way to “determine the circumstances of the incident and locate any suspects” after it was made aware of the video yesterday.

A spokeswoman for the Met said: “Police are aware of a video circulating on social media appearing to show the theft of a bike and threats being made against a member of the public in Westgate Street, Hackney.

“At this time, no report of the actual incident has been made and no victims have come forward.

“Anyone with information is asked to contact officers in Hackney on 101, or to remain 100 per cent anonymous, please give information via the charity Crimestoppers: 0800 555 111/crimestoppers-uk.org.”