Armed officers and sniffer dogs stormed the home of Kai Agyepong in Camden on July 17, after responding to reports of a male holding a firearm. Kai’s mother Alice Agyepong condemned the police and said her family felt "utterly violated" and feared for their lives during the late night ordeal. She said the Met had thrown "every single resource except a helicopter" at the incident.

Ms Agyepong, who also has two daughters living at home aged 16 and 23, said: “In my mind there was no question they were going to shoot us.

"Their guns were drawn in such a way they were aiming their rifles at me and my kids."

Even after being shown the BB pistol fitted with a blue slider to distinguish it from the real thing, the police conducted a full search of the premises lasting more than an hour.

The horrified mother said the Met had explained the incident by saying senior gang members often leave knives and firearms with younger boys.

Former shadow home secretary Diane Abbott hit out at the incident.

The Labour MP wrote on Twitter: “How can the Met Police possibly justify arresting a 12 year old at gunpoint, handcuffing him & putting him in a police van? This after dozens of armed police officers raided his home at 11.00 at night.

"All over a toy. Is this what they call community policing? #BlackLivesMatter.”

Commander Kyle Gordon, the Met's lead for firearms, said the force takes “every report of a firearm seriously” and insisted officers “acted in line with their training”.

Commander Gordon said: “There have been a number of well-publicised shootings in London in recent months where members of the public have been injured.

“As the public would rightly expect, we take every report of a firearm seriously in order to protect our communities.

“Officers attending reports such as this must treat them as genuine until they can verify whether or not an actual firearm is present.

“Based on the information at hand, the officers acted in line with their training and my expectations, enabling the incident to be concluded as quickly and safely as possible.”

Commander Gordon said he had watched the body-worn video of the incident and said he was “content” with the officers' professionalism and how they had explained to residents what was going on.

The Met chief said Kai was immediately let go as soon as officers had established the only weapon in the house was the BB gun.

He added: “The reporting member of the public was right to call us and we would encourage others who see similar weapons to do the same.

“We are committed to bearing down on violence and we rely on our communities to help us do this.”

The Met has referred the incident to the Independent Office for Police Complaints (IOPC).