A group of teenagers huddles under the grey London sky. It is 4pm and the light is just beginning to fade. The group is well dressed – in Nike, Adidas, Sean John – and they mutter to each other in a language barely intelligible to any adult. Occasionally, they all bellow with laughter and furiously flick their fingers, in an acknowledgement of one member landing an especially ingenious insult on another.

They constantly check their phones, all BlackBerries (BlackBerry Messenger keeps them in touch free of charge), and type furiously. By 11pm their number has swelled considerably.

"What do you think they are all waiting for?" I ask one of them, Kieran, and he shrugs. "Life, to start, man. Do you know what I mean? I mean this wasn't the f******* way it was supposed to be. This wasn't on anyone's wish list."

Download the new Independent Premium app Sharing the full story, not just the headlines

But this group is waiting for something: a bus. For these boys, it is not really a means of transportation. Tonight it's a bed, a shelter, a home, a refuge. "Bussing" is becoming a phenomenon in Britain, a grim choice for kids who, while not exactly homeless, are mostly not allowed or are too scared to go home very often.

Unknown quantities of teenagers are spending their nights on buses, which are cheap (less than £5 on an Oyster card will get you around all night), instead of in a warm bed.

Official statistics on bussing do not exist. But children's charities are aware of the extreme measures that exiled teenagers are taking to stay off the street, particularly at night.

"There are so many teenagers in peril," said one charity worker, "that the ones who have an Oyster card, a jacket, even a place to go for a few hours in the day to change or sleep, won't be seen as a priority by the Government, social workers or, indeed, charities."

I heard about bussing from several kids I encountered while teaching and was interested in learning more. But it's a difficult world for an adult woman to penetrate. The young people who do it don't trust adults, and to just jump on board and try to chat would be foolhardy.

I met Kieran through a professional acquaintance. He is a tightly wound, intimidating young man who moves like a feral cat and has a look that could melt lead. However, once he warms to you, which takes a while, he reveals a very different side: bright, funny, articulate – charming, even.

I asked him to be my bussing guide for two reasons. First, he is very much representative of the teenagers often portrayed so negatively: no GCSEs, few job prospects, somewhat alienated from society and arguably in danger of turning to crime. He is one of many young people for whom education is no longer even a potential route out of the grinding poverty of our inner cities. As he sees it, education is just not an option.

Daily coronavirus briefing No hype, just the advice and analysis you need Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive morning headlines Monday - Friday plus breaking news alerts by email Update newsletter preferences

Second, he is scary. He is easily the most streetwise of this relatively young group (they are all under 18). When I ask him what happens when they encounter older groups – the ones who have succumbed to much harder crimes, drugs and lives – he gives me "that look" and says: "We mostly don't. We know the routes really well." The others all nod, their faces a combination of fear and aggression.

I have promised to keep their route secret, a condition I don't quite understand at first, but it's a complex and busy path that is often aborted or changed at the drop of a hat – the hat being variously police, zealous transport workers or, most dangerous of all, other lost, roaming teenagers deemed to be foes rather than friends.

We board in North-west London on a regular bus, with the intention of heading into the heart of the capital, where there is a much greater choice of night buses when it gets later and colder. By now the teenagers seem to have fully accepted my presence and are keen to tell me about their lives. The most pressing question I have is: why? Why would you eschew safety and warmth and comfort for this? It turns out that, while a couple of kids might be along for the ride, for most this is their only option.

A boy with huge brown eyes, so small he barely looks older than 12, tells me: "I'm allowed home in early mornings to have some food and change my clothes, but I have to be gone by the time my mum wakes up." When I ask him why, he shrugs, as if the answer is forgotten or irrelevant.

Another tells me that if he stays at home he "gets into more trouble". I ask him how so and he seems reluctant to answer. Kieran looks up from his phone and says, not without compassion: "His brother is really bad news. Because Rob has such a baby face, his brother is always trying to get him to hold stuff or pick up stuff for him, because he's less likely to get lifted." Rob nods, looking embarrassed.

What about your parents, I ask. The question is instantly met with a cacophony of teeth-kissing and cursing and other noises to suggest that their parents aren't exactly fulfilling their roles satisfactorily. I ask if they feel part of a family, keeping each other safe. Everyone nods. "No one gives a f*** about us but we look out for each other," says the little one. "Shut up, man," says Kieran, but he is sort of smiling.

Suddenly, for reasons unclear to me, we have to get off the bus. When we have boarded another, I ask why. They spotted another bussing group with whom they have "beef" and thought they might board.

I ask how common bussing is. They all clamour to answer, yelling over each other, and I make out "Loads!", "But we started it!", "F****** Polish, man!" This is the first of many negative references to the Polish (I think they more broadly mean eastern Europeans). The eastern European presence on what they consider to be "their territory" makes them very uneasy.

"Shut up!" thunders Kieran and they all do, ever deferential to him. "Loads," he tells me. "Loads. And it's being taken over by loads of other groups." But he is either unable or unwilling to tell me who these others might be.

I ask why so many people are riding night buses. They all start bellowing again, keen to share their theories, but it's the small, brown-eyed boy who has the most compelling one. "It's legit, man. If you are in a shopping centre or even the f****** street, you can be moved on by anyone. But if you have an Oyster you've got a right to be here. No one can say s***."

They also feel safer. Kieran says: "From here you can see trouble coming. You're less of a mug." The notion of the bus as a watchtower both amuses and saddens me.

So do girls ever join them? Their shrieky answers suggest that they probably do, but despite their outrageous "playa" boasts, these boys are still at an age where, really, they are a bit scared of talking to girls.

When I ask how many of them feel they messed up at school, most admit to it immediately and express regret. It's a heartbreaking paradox that teachers and parents will recognise: so many kids get it just that little bit too late.

A few talk half-heartedly about doing something at college, but the very small boy says: "What's the point? There are kids coming out of school with 11 A*s and not being able to find a job. Who's going to give us a job?" None of them can remember what they wanted to be when they were little.

Suddenly, there is much shrieking and the boys clamber to get a look. They bang the window and hoot. After a few hours of bussing, we have found ourselves near King's Cross, still home to street prostitutes. "That's nasty, man," says one. "Can you ever imagine being that desperate?"

I ask if they'd consider a visit to the job centre. They all shout with laughter and flick their fingers. "My friend says he knows someone who caught HIV from the job centre. It's a nasty place, man!" cries one of them. When the hilarity has died down, Kieran, still attached to his phone, says: "I've got more chance of meeting Elvis than getting a job there." "Who's Elvis?" asks his friend. "Some dead brother," says another. Kieran kisses his teeth. "Elvis was white, he just sounded black. Like Eminem."

It's getting on for 3am and Kieran announces they will be getting off in a bit to "take care of something". I don't care to find out what he means but it reminds me to ask about crime.

There are vague, reluctant murmurs, with the vociferous defence that "crime is becoming the only option". I ask about the London riots and most get a look on their faces, like old hippies do when asked about Woodstock. The small one says angrily: "That was three f****** nights of the year my mum made me stay in!"

Names have been changed. The full version of this article appeared in 'TES' magazine on 4 January