Richard Santos was driving down Clapham High Street on Tuesday evening when the traffic came to an unscheduled halt.

It was around 7pm, and the 49-year-old, who'd just finished work at posh local butcher's shop M Moen & Sons, watched helplessly from behind the steering wheel as his Kia Sportage was suddenly, and unexpectedly, surrounded by feral youths.

'I wasn't sure what was going on,' he recalls. 'There were all these kids around, and the police were trying to get them out of the road.'

The mob wore a sort of uniform: expensive trainers, dark tracksuits and hooded tops. Several had covered their faces with balaclavas or masks. And a large number were filming proceedings on mobile telephones.

'I saw a girl punch an officer in the face. Then there was all this screaming and shouting, and everyone ran towards the noise. I just thought to myself: 'What on earth is happening to the younger generation?'

What was happening was very simple: the streets of Clapham had become the scene of a 'link-up', a social media trend in which large groups of teenage children arrange to meet at a particular time in a specific location, usually in a major town or city.

Once there, the crowd will typically swarm up high streets, running through the doors of shops and fast-food restaurants. Ringleaders then fight or shoplift food and drink. A small number might attack however many (invariably outnumbered) police officers are sent to restore law and order. The remainder will make videos of the whole thing and post them to TikTok.

Tuesday's proceedings had begun on the basketball courts on Clapham Common. Around 300 youths turned up after reading messages on the social network Snapchat telling them to arrive at around 3pm. Plans were shared on other social media sites using the hashtag #claphamcourtslinkup.

The ensuing carnage, which lasted for almost seven hours, saw five people assaulted, including four police officers, one of whom ended up in hospital.

Three girls, one of them 17 and the other two 13, were arrested on suspicion of theft and assault outside Sainsbury's, where the front door was barricaded shut and terrified customers had to be escorted out via a loading bay. It took more than 100 officers to bring things back under control.

By the time the whole thing was over, several fires were burning on the Common, where various youths had also launched fireworks, and various roads and pavements had been covered in looted white paint.

The lawlessness marked the second time in just four days that Clapham has been targeted. A similar incident, at around teatime on Saturday, saw the local M&S looted. Police were forced to issue a dispersal order and two 16-year-old girls and one 15-year-old girl were arrested for shoplifting and assault.

At Common Pizza, a food and drink joint which backs on to the basketball courts where both events unfolded, manager Ismail Haden, 23, said: 'Last Saturday we were open and all of these kids turned up who were only between 12 and 16. It was kids being kids, fights breaking out. But yesterday [Tuesday] was even worse.

'Some customers who had wanted to use the court to play basketball left their bags with us for a bit, as they were scared to bring them. Then they ran back here telling us they had seen kids with machetes and Rambo knives. We shut everything at 7.45pm.'

Recent chaos wasn't confined to south London. Similar scenes were witnessed in central Birmingham on Friday afternoon. Huge mobs of teenagers, whose schools had broken up for Easter that lunchtime, descended on the streets around the Bullring shopping centre and began swarming into fast-food restaurants.

One viral TikTok film of proceedings, titled 'Police have lost control', shows groups of officers in hi-vis coats trying and failing to disperse the crowds.

Another, depicting several youths being arrested, is captioned: 'Saw someone's weave [hair extensions] get thrown'.

Solihull was also targeted on Tuesday, with West Midlands Police forced to issue a 36-hour dispersal order in the town centre due to 'a number of incidents of antisocial behaviour', including 'reports of children and teenagers causing antisocial behaviour and criminal damage'.

The wave of incidents is being fuelled by a host of factors, including a spell of reasonably clement weather plus the fact that tens of thousands of secondary schoolchildren (especially those who – for whatever reason – aren't inclined to spend Easter revising for upcoming exams) are now on holiday, so have very little to do all day, aside from twiddle their thumbs.

Also to blame are social media companies who, by either accident or design, have created platforms that provide a perfect medium for organising 'link-ups'.

Snapchat forums, which are essentially large member-only chat rooms similar to WhatsApp groups, are where most of the recent flash mobs seem to have been planned.

Not only can messages be exchanged anonymously in the forums, which are hugely popular among teenagers, but they are also designed to self-delete after 24 hours, making it nigh-on impossible to hold ringleaders to account.

With regard to the #claphamcommonlinkup, investigations by the Mail have established that Tuesday and Saturday's events were arranged via a number of different groups containing hundreds, and in some cases thousands, of teenagers in south London.

Two of the most active chats appear to have been set up by students at a pair of large secondary schools in nearby Brixton: Trinity and Ark Evelyn Grace academies. Both are within walking distance of the Common.

Police appear to have infiltrated at least some of the groups. Shopkeepers in and around Clapham were contacted on Tuesday and advised to either close their premises early or take precautions to protect staff and customers.

'Police told us to shut our shop and after we re-opened we were warned not to let any kids come in today,' said an employee at Roosters Spot chicken shop on the High Street. 'We were scared because we heard groups of ten to 15 of them were coming into shops, running about, picking up trays and smashing stuff at walls.'

It should, at this stage, be stressed that only a small minority of attendees at both events committed acts of violence, or took part in shoplifting.

Despite the striking footage of crowds invading a local McDonald's or swarming past parked cars, most of those present simply watched, and sometimes cheered, as the whole thing unfolded.

But that is, in its own way, part of the problem. For many of these bystanders spent their time taking videos of whatever trouble ensued. These were then uploaded to TikTok.

The video-sharing social network is crucial to understanding where the 'link-up' phenomenon may now lead, because clips of the chaos in Clapham and Birmingham have generated large numbers of 'likes', which in turn is fuelling appetite for a repeat performance.

'We go again on Saturday', declared a user named 'Cece', who appears to be a teenage girl from south London and posted a string of clips of Tuesday's proceedings. Another 'creator' who filmed the carnage outside Greggs commented: 'I'm tryna get my likes up bro.'

Some of the most successful footage was shot by Matt Khan, an innocent bystander who was stuck inside the Chicken Hub takeaway next to Clapham's Inferno's nightclub as a crowd descended on the High Street.

He generated more than two million views for his striking videos depicting a couple of youths being arrested for shoplifting outside the local Sainsbury's.

Another tranche of clips was shared by the youth wing of the Taking The Initiative Party [TTIP], a Croydon-based political party that was originally founded by Sasha Johnson, a prominent Black Lives Matter activist who has called for the police to be defunded. It's not entirely clear why TTIP, which is putting up a number of candidates in forthcoming elections, was present at Tuesday's 'link-up'.

But its young supporters appear to have been close to the action throughout much of the carnage that unfolded on Clapham High Street. Many of the videos that then circulated on TikTok contained footage of them expressing disapproval of what they were witnessing, and intimating that the party would help restore social cohesion in areas affected by such scenes.

Though this week's events have thrust the 'link-up' phenomenon to prominence, similar incidents have, in fact, been taking place for a number of years. In the summer of 2024, I witnessed one while walking through Piccadilly Circus early in the evening.

Out of nowhere, several hundred youths, blowing whistles and screaming, ran into a branch of McDonald's. Several of them jumped over the counter and began helping themselves to hamburgers while terrified employees cowered in the kitchen.

In February last year, a similar incident unfolded just a few blocks away, on Broadwick Street in Soho, where a flash mob of schoolchildren took over an unattended police car, chanting 'f*** the feds'. Footage showed hundreds of youngsters gathered around as at least ten boys, some wearing stolen police uniforms, hijacked the vehicle.

Still uglier were scenes a month earlier, when a gang of hooded youths descended on the Apple store at north London's Brent Cross shopping centre.

Mobile phone footage showed roughly eight of them, all dressed in black, using the chaos to grab iPhones and iPads from display desks, before fleeing the premises.

Perhaps understandably, the ongoing trend has sparked political point-scoring. Tory leader Kemi Badenoch yesterday dubbed the scenes a response to the 'total collapse of consequences'.

'Children smashing up shops in broad daylight, stealing and even filming themselves doing it as if it were a game, is a much bigger problem than is being recognised – this is a total collapse of consequences,' she said.

And addressing online commentary which pointed out the significant number of black teenagers involved, she said: 'To those making snide comments about race or black kids – you do not see scenes like this in Lagos or Nairobi. Not because the children there are different, but because actions have consequences.

'There are clear boundaries. Parents, communities and the authorities do not wring their hands or look the other way.

'Here, we have created a culture where too many young people believe they can do what they like and nothing will happen.'

Sir Sadiq Khan, the Labour Mayor of London, finally responded to the chaos yesterday, saying: 'There will be an increased police presence in the area in the coming days, with officers providing support and reassurance to residents and businesses.'

Whether that will deter the flash mobs, who plan to return on Saturday, is anyone's guess.

Back at the Common, Richard Santos, who moved to London from a crime-ridden corner of South America 20 years ago (and now has a 14-year-old daughter at a local school), certainly isn't holding out much hope.

'I'm from Brazil, a place where everyone knows there are rough areas and criminality,' he says. 'But things like this make me think it's not as safe here as I had pictured.'

•  Additional reporting by Kristina Wemyss.