A teenager has described the moment he stabbed his mother’s “violent” ex-boyfriend to death in what he claims was self-defence, using a martial arts move he learned on a top secret Army training camp where he was pretending to be a terrorist.

Chevaughn Chin, 19, is accused of murdering 39-year-old Jerome Scott at his Hackney home in Ribstone House, Morning Lane, after the older man came looking for Chin’s mother Tameka Belnavis on October 18 last year.

Jurors at the Old Bailey heard how Chin, who was 18 at the time of the incident, let Scott – who he “trusted like his father” – into his home.

But after Chin saw him crouching “suspiciously” at the door of his mother’s bedroom, where she was lying in bed with another man, he asked Scott what he was doing, he claimed.

He alleged Mr Scott then pulled out a knife and held it near his face “aggressively”.

Chin, who went to a specialist sports training college and had dreams of becoming a professional boxer, said: “I was shocked and I didn’t know what was coming next.

“If someone has a knife in my house and looks aggressive, I don’t know what he’s going to do next, who he’s going to harm. My instant reaction was to grab his hand.

“I grabbed his wrist underneath the knife with my left hand, and with my right hand I grabbed his elbow. He was pushing the knife towards my face. He kept pushing.

“I was pushing as well. I had to use more power and force to push the knife away.

“He gave way and my power overcame his power and the knife went into his chest.

“I hadn’t intended in any way for him get hurt. I was scared and terrified of what had just taken place.”

Forensic pathologist Olaf Petrovski described how “severe” force must have been used for the knife to pass through Mr Scott’s breastbone and into his heart.

Doctors at the Royal London battled to sew up the damaged organ but he was pronounced dead at 11.40pm.

Chin claims learned the Wing Chun martial arts move, designed to disarm an armed attacker, just four months previously on a top secret training camp for the Army, where he was tasked with enacting potential real-life threats.

Although not part of his official job there, which he had to sign the Official Secrets Act to carry out, he asked his team leader – a martial arts expert – to teach him the move one night outside the hut where they slept.

Jurors at the Old Bailey have heard how Mr Scott, whose nickname was Skinny, had a history of being violent towards his ex-girlfriends, with “a number of them” filing five reports to police that he had bitten them, broken their furniture, damaged cars and threatened one with a knife.

Mr Scott, from Walthamstow, had no defensive injuries associated with fending off a knife, it was said.

Chin denies murder. The trial continues.