A schoolboy pleaded guilty yesterday to hiding a Baikal semi-automatic pistol — regarded by police as “the gun of choice” in gangland Britain — in his family’s cellar.

The boy, who was 13 when he was arrested, had wrapped the weapon and two silencers in bags and a pillowcase and put them in a rucksack before concealing them.

Police searching the Victorian terrace house after a tip-off also found 31 rounds of 9mm ammunition in one of his socks and a machete hidden in his wardrobe.

The police raid, in August, ended an eight-month period during which the boy had been sucked steadily into the gang culture of southeast London. Since January he had been excluded from school, received a youth court referral for carrying a meat cleaver and been given warning notices for robbery and using threatening behaviour.

Judge Usha Karu, sitting at Inner London Crown Court, told the boy that the firearms offence was so serious that it was “almost inevitable” that he would receive a custodial sentence.

The loss of the gun has also placed the boy “in mortal danger”, making him a potential target of a gang.

The boy, who cannot be named because of his age, has cut a vulner-able figure during a series of pre-trial hearings in recent months. Wide-eyed and apprehensive, he stood in the dock, zipped up in his black school anorak and casting anxious looks at his mother in the public gallery.

A middle-aged woman with a respectable job, she attended each of the hearings, bringing soft drinks and sweets to be passed to him while he was being held in the cells.

“He’s just a boy,” his mother said. “He didn’t understand the seriousness of what he was getting into.”

The woman had protested angrily when police arrived on her doorstep in New Cross on August 12 with a search warrant. She accused the officers of planting the machete but was said to have been stunned when they found the gun.

The boy claimed that he had been forced to hide it for an older gang member, possibly as part of an initiation rite or to earn promotion, but also admitted previously hiding other firearms. He did not, however, name the gang or identify the person who ordered him to conceal the weapon.

Police believe that he is in the junior ranks of one of the nine gangs involved in serious crime in the Deptford and New Cross areas. The largest of these is the Ghetto Boys, which has been active for more than ten years.

Detectives are understood to have advised his mother that the only certain way of protecting her son’s life and preventing him from being lured back into a gang is to leave the area.

The boy has been released on conditional bail pending sentence on January 30. He must live outside the borough of Lewisham, have no contact with a list of named individuals and abide by a 7pm-7am curfew. He may not own a mobile phone and can use one only in his mother’s presence.

One source told The Times: “He doesn’t look the part — he burst into tears in police interviews — but he is now part of the tangled web. He lost the gun so he’s in debt. He has to make up for it financially or he becomes a target.”

Sources said that the gun would have been acquired by an older gang member, probably in his twenties, and passed to the youngster to store in order to evade the mandatory five-year sentence for firearms possession that applies to adults.

The source added: “A few years ago it was all people in their mid-twenties. They are still involved but they’re overlording it and there are more teenagers involved. It’s got more chaotic as it gets younger.”

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