Social media has been singled out as a key issue amid the rise in teenage violence in the capital.

Experts say disagreements are exacerbated when played out online, and that the amount of violent content has helped normalise aggression.

It comes as the fatal stabbing of a 15-year-old boy in Croydon, south London, became the 29th teenage homicide in London in 2021, which surpasses the 27 seen in 2017, and equals the previous peak of 29 teenage murders in the capital in 2008.

Junior Smart, founder of the St Giles Trust SOS Project that helps divert young people from crime, said technology giants should be asked to invest profits into areas blighted by violence.

He told the PA news agency: “Violence has been normalised, especially over the last 10 years through social media.

“It’s a crazy situation here where if a person goes to a live event and starts livestreaming music they will be silenced and perhaps have a sanction, whereas someone can be online posting violence and use the p word or the n word or a load of expletives and nothing actually happens.

“The reality is that social media platforms have got a lot to answer for. In practically every situation where we’ve seen violence happen there has been some sort of connection with an online platform in some form.

“Why are these social media platforms not being held to account? Why are we so scared of asking really difficult questions and why are these social media platforms not putting more money back in the communities that are being affected by violence?”

Jon Yates, executive director of the Youth Endowment Fund (YEF), said there are three factors behind the rise in violence: an increase in the number of children who are vulnerable, for example in care or excluded from school; increased pressure on services such as policing, mental health and youth work; and social media fuelling conflict.

He told PA: “We don’t fully know the impact of social media. But any young people I talk to say that social media and the fact that something they say in passing becomes written down, causes what might have been nothing to become something.”

The YEF, funded by the Home Office, was set up to scientifically evaluate schemes to reduce youth violence and push for the adoption of the most effective.

Its online toolkit, providing an at-a-glance guide to what works best, currently rates cognitive behavioural therapy as highly effective, as well as focused deterrence schemes where young people have their housing, training and employment needs met as long as they stay on the right side of the law.

However military-style bootcamps for young people who have been convicted of a crime have been found to be actively harmful, as have prison visits to inspire fear of the consequences of being caught.

“This is not a one-off, one year problem,” Mr Yates said. “The actual number of young people who die tends to vary but the number who are being seriously injured has been going up for a number of years, right back from 2013. In many cases the difference between a serious injury and a fatality is millimetres.

“If we’re serious about making a difference the solution is obvious. We’ve got to find out what works best, and then we’ve got to execute it.”

Domestic abuse has long been recognised as an aggravating factor in young people becoming involved in violence in later life, and new research suggests it may also be linked to extremism or terrorism.

Mr Yates said: “For most young people in this country violence isn’t at all normal, but there is a proportion whose lives are far too full of violence.

“Part of that is social media, but lots of it is their day to day lived experience, of having friends or friends of friends seriously injured.

“The most important thing we can do, particularly those of us who live relatively safe lives, is get much better informed about what works to make a difference.

“We know that for a child to witness domestic abuse is a risk factor, it makes them more likely to become involved in violence.

“What we don’t know is what’s the best way to address that.”

Mr Smart, who was himself jailed for 12 years for a drugs crime and is now a youth work expert studying for a PhD, believes there needs to be a reduction in bureaucracy in agencies that help the young.

“I’ve gone into meetings and I’ve spoken to people round the table, great organisation, everybody trying their real hardest.

“I’ve worked it out and I’ve said how long have you spent with the young person or the client since the last meeting?

“And we’ve been in the meeting longer than they’ve spent with the client. How does that make sense?”

He says that poverty is a key driver of violence, and a lack of trust among young people of those in authority.

“They talk about adopting a public health approach but if that was the case we’d be inoculating the youth against violence, can you see that happening? It is absolutely not happening,” he said.

“Why would we expect a young person to go to a police officer or go to a teacher when every single experience they’ve heard of in the past or they’ve experienced themselves says ‘do not trust this person’?

“The violence is an epidemic, but here’s the thing. Just like that virus, it is preventable.”