Elite armed officers broke up a teenager’s house party at a Wimbledon Village mansion on Friday.

More than 100 revellers spilled on to Wimbledon Common as officers form Scotland Yard’s Trojan unit responded to claims some party-goers were armed with knives.

A large group of teens was turfed out of the £2m detatched property in Lingfield Road and soon surrounded unarmed Merton police who arrested a 15-year-old for assaulting an officer just before 10pm.

Three Trojan officers – who are usually armed with pistols, MP5 sub-machine guns and Taser guns – found no offensive weapons at the scene, according to police.

Witnesses said homeowners attempted to prevent gatecrashers from entering the party before the group gathered around a police van and car, chanting at officers called to disperse a crowd from the common.

Riot police from the Metropolitan Police’s riot squad were on stand-by but officers from Merton managed to dispel the crowd by 10.30pm.

The 15-year-old was later “de-arreseted” before being taken home, but police are investigating claims £1,200 of electronic equipment, including an iPhone and digital camera, was stolen from a bag belonging to another 15-year-old at the party.

Homefield Road resident Gengez Reza-Khan, 28, said: “I was on the common near the war memorial having a quiet drink with friends when a swarm of adolescents appeared from Lingfield Road.

“They weren’t particularly making a nuisance of themselves, but then the police cars circulated and things turned ugly. We saw one young person bundled into the back of a car, and then the police were surrounded.

“Back-up arrived and there were more officers in a van. It didn’t seem an entirely disproportionate response until we saw armed police outside a house in Lingfield Road. It was unbelievable.”

One teenager who did not wish to be named, told our reporter at the scene: “I heard someone brought a knife to the party but this is crazy.

“I just don’t know why there are so many police here. We’re all going back inside when they’re gone. This is just mental.”