Sean, 19, saw three people stabbed growing up in an English city. He went to a failing school and sometimes endured poverty, heating bathwater in saucepans and eating sugar sandwiches. Now he is one of thousands of youths negotiating byzantine gang rivalries and coalitions whose subtle shifts can mean the difference between life and death. Violent disputes involving knives and guns blow up over the lucrative cannabis and cocaine trade as well as “beef” spread through music and video clips on Instagram and YouTube.

“On that corner right there I saw someone I knew get his face carved,” Sean (not his real name) said as he gave the Guardian a tour of his area. “Someone carved their initials on to his face because he was shottin’ [selling drugs] in here. He’s been warned before and he was there again. It was deep.”

Fear – including what youth workers describe as hypervigilance – is ever-present. When his mother wanted him to wear a coloured top that she didn’t realise would mark him out as affiliated to the wrong gang, Sean bawled his eyes out because he feared he would get “clacked”. He froze when a car pulled up 20 yards away in case it contained a threat. Local youths had circulated a song on Instagram that attracted nearly 100,000 views but angered rivals who were now thought to be out for revenge.

“It all starts off with defence,” he said. “There are a few psychopaths out here but that’s a small minority of people that want to just kill. A lot of people in gangs are normal people. They have morals. They are just defending themselves and it gets to the stage where self-defence isn’t always when someone attacks you.

“Someone can know where you live and where your mum stays and then you have to take action on that. Pre-emptive strike. You’re not just going to sit around till they come so when they bust a shot through your window, you can shoot back.”

Fear and pride drive the violence, he says, quoting the aphorism: “I’d rather be judged by 12 [face trial by jury] than carried by six [end up in a coffin].” One person he knows regularly wears body armour and straps a knife to his leg.

“When people have big knives strapped to [themselves], is that going to make you want to take a kitchen knife or a little flicky [a spring-assisted knife]?” he asked. “You’re going to want a big knife so you can defend yourself against a big knife.”

And now guns – shotguns, handguns, submachine guns – were becoming more prevalent in gangs, purchased with healthy profits from the drugs trade, he said. Police records of crimes using firearms in England and Wales show an upward trend since 2013, after years of reductions.

“Instead of one gun between five people, it’s one MAC [submachine gun] between two people.”

Local disputes spread virally and nationally, he said. People in smaller towns follow events in his area through videos of attacks shared online and through songs referring to them.

“In Darlington, if an impressionable kid stumbles across a music video and they [wonder why] they are talking about waps [guns] and shanking [stabbing] … they are intrigued by this new world. They start to learn, they follow the social media account but they don’t see the reality of it.

“They might see a video of someone being stabbed but you can get desensitised to it over a screen. They’ll start dressing like it, having their trousers around their hips and eventually they’ll be like ‘why aren’t I carrying a knife?’ ... That’s what people don’t understand. It’s not only a black problem, a working-class problem.”

Sean says he has “a very bleak outlook” and that while he agrees gangs can be a substitute for family, it’s “not something we can change”.

“That’s just how society is for a lot of working-class people,” he said. “They don’t have father figures, or they have drug-addicted parents.”

Gang culture, he concludes, is like a wine stain on a rug. “You can try and get the stain out but it’s not going to go,” he said. “You might move a sofa over it. It’s entrenched. It’s something we’ve got to live with now. There’s no solving it.”