A mass of legs and arms, some clutching bats, sticks and metal poles, many wearing school jumpers, swarms around a barely visible form on the ground. The appalling footage of the brawl that brought terror to the streets of London this week shocked many.

Witnesses told of armed boys being cheered on by foul-mouthed girls filming the violence on their phones.

"It was like nothing I've ever seen before," says Jeanne Asquith, a company administrator who watched in horror as the violence erupted outside her house.

As police helicopters circled, officers from the Metropolitan Police's Territorial Support Group arrived in riot vans to deal with the hundreds of children involved.

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Two teenagers needed hospital treatment, and a further seven teenagers and young adults were arrested for their part in this shocking and apparently spontaneous outburst of street violence in the London borough of Bexley.

Most disturbing, however, was the handful of parents said to have turned up to enjoy the spectacle on Monday afternoon. Some were said to have encouraged the fighting. One witness claimed to have seen "parents giving out hammers and bats".

At the height of the ruckus, a silver Mercedes drew up beside the fighting children and a father stepped out. His first act, onlookers noted, was to hurry his teenage daughter into the car where she remained with her mother. He then opened his boot and took out what looked like a golf club.

Moments later he disappeared around the back of the bowling club on Bexley's Northumberland Heath, where hundreds of schoolchildren, some still in their uniforms, had flocked.

But while the police and schools have sought to calm fears in the aftermath of the unrest and have promised extra patrols in the area, those living at the heart of this suburb are warning of a deep-seated new malaise emerging among young people and their parents that has clear implications for the rest of Britain.

"These kids were feral; completely wild. Who is raising them to be like this?" says one woman, a Neighbourhood Watch co-ordinator who lives on the edge of the park where the battle took place. "It's very, very frightening. If it can happen here, it could happen anywhere."

Her words proved prophetic; a day later, a similar incident took place in the centre of Manchester involving up to 100 children. Police received emergency calls at around 7.20pm, but by the time they arrived, the children had disappeared.

So what happened in this London suburb last Monday and what, if anything, can be learned from it?

Police are still investigating the violence that erupted in several flashpoints in the area. Ironically, Bexley was recently named the second safest of London's 32 boroughs in terms of recorded crime. It has relatively low unemployment and higher than average GCSE results.

And yet there is talk of racial tensions and grudges between gangs, fuelled by boredom and discontent, as well as rivalry between schools including Erith School, St Columba's School for Boys and Woolwich Polytechnic School for Boys.

Whatever the causes, the scale of the riot was achieved thanks to youngsters on social media, inciting others to come along and whipping up a frenzy.

As with the summer riots that afflicted Britain in 2011, they used apps where messages self-destruct, as well as encrypted and free texting apps. As word spread, they used the free travelcards issued to under-15s to travel to hotspots. Some of those involved also used the social media label "#5w", standing for "five words" - which are the ominous: "We go where we want."

The first signs of trouble emerged at about 4.30pm at Clocktower Square in the Broadway, Bexleyheath's main shopping area. Even on a normal day, hundreds of pupils from schools in the area congregate here to catch buses home. There were rumours that teenagers from rival gangs were meeting to fight after the brother of one of them had been attacked.

On school days, police officers stand in the square to keep an eye on the children and to encourage them to move swiftly on to buses and out of the area. On Monday, however, shopkeepers noticed a growing crowd of children.

"There were over a hundred of them when I saw them at about 4pm," says a worker from McDonald's, which overlooks the square.

A restaurant worker says: "I saw some of them rush off down towards the fountain and I thought maybe there was going to be a fight."

There were skirmishes. The handful of police chased the perpetrators. Within minutes, dozens of children had piled on to buses heading up the road towards Northumberland Heath two miles away.

As fighting broke out by bus stops on the main shopping street, shopkeepers locked their doors and police tried to get children back on to buses leaving the area.

Shopowner Chantelle Devereaux, 59, describes the gang of youths as "frenzied" and says: "Even the girls were getting involved."

Some were seen taking broken bricks and wooden batons from skips in roads leading up to the heath and handing them to the boys. At around the same time, five miles away, children were congregating in the shopping square by Woolwich Arsenal railway station, a large open space with outside seating and takeaway restaurants, as well as a giant outdoor TV screen.

A town centre warden says: "There were kids from four or five different schools. Hundreds of kids come through here each day after school. Sometimes they fight; it's one of those things that happens and it's happening more frequently."

Teenagers from Woolwich were also seen heading to Bexleyheath and then to Northumberland Heath, a sleepy place with a village-like atmosphere. After school, however, the parkland is transformed. For years now, it has been dogged by antisocial behaviour and drug-dealing in the evenings and at night. The ground around the rugby club and the neighbouring bowls club is littered with silver nitrous oxide canisters - so-called "hippy crack".

A former teacher from nearby Erith School says: "They take drugs round the back of the rugby club. The problem seems to be getting worse. The older ones are influencing the younger. They shouldn't be here at all. Why don't their parents make sure they go straight home?"

However, parents seem to be few and far between. Mel Hudson, 42, a community outreach worker, says: "A lot don't have parents at home waiting for them. No one is looking after them. They're too old for childcare, but too young to be left unsupervised. Youth clubs have been closed because of a lack of council funding. Adults created this situation and we're going to pay a heavy price."

Racially motivated gangs have long existed in the area. The initials of a white gang called Racial Attack or 'RA', is splashed on the walls of the rugby club.

T-Block, a black gang from Woolwich, was said to have been involved on Monday. Territories are fiercely guarded by boys seeking 'respect' from their peers. The "North Heath boys" are particularly possessive about "their" park and there is speculation that on Monday, a black gang may have strayed into their area.

Bonnie Lampard, a 23-year-old barmaid, says she saw a large group of white boys: "They had balaclavas on and some were wearing scary Halloween masks."

She says that, moments later, about 50 black teenagers arrived at the park: "They had metal bars, knuckledusters and knives."

Seven people aged between 15 and 21 were arrested and released on bail pending further inquiries.

Tensions are still running high. Extra police have been patrolling alongside a mobile CCTV unit filming pupils as they congregate at bus stops after school, but rumours are already circulating on social media of a rematch, possibly in nearby Crayford, next week.

It would be easy to dismiss Monday's clashes as an isolated set of circumstances, but the events in Manchester suggest otherwise. The St Giles Trust works with young people at risk of violence and says there is a "growing problem with gang-related issues".

Community worker Mel Hudson says: "Parents need to spend more time with their children."