Earlier this year, I wrote for TES about children in the UK who travel on night buses to stay off the streets ("The journey with no destination", 4 January).
One criticism that the article attracted was that it didn't feature any girls. This wasn't intentional. In my research, I found that the girls were much less visible - and much less forthcoming. The boys were perversely proud of their Hardy Boys meets The Wire existences, whereas the girls radiated a scared, ashamed silence.
To find voices in that silence, I start by visiting two charities - one in London, one in the North of England - that work with young people who are struggling with drug and alcohol dependency, homelessness, domestic violence, unemployment and other problems.
"I went through the classic cycle," says Katie*, a thin, fragile young woman of 17. "Kicked out of home, got into drugs to cope, met a guy who was abusive and acted as my pimp even though I didn't realise it - I thought he was my boyfriend. He eventually kicked me out when I fell pregnant and he realised I couldn't make him any money any more. Most men don't want to have sex with a pregnant woman. And definitely won't pay for it."
Among the girls and women I spoke to, a recent past of sexual exploitation was a recurring theme. "A lot, if not all, of the women we deal with have some experience with this, from an abusive 'boyfriend' to full-on prostitution and being pimped," the director of a well-known charity says.
Part of the problem is the legal grey area that some of this sexual exploitation falls into. The victims - almost invariably young, vulnerable girls - don't see it for what it is, or see it too late. Another charity worker tells me how anxious they are to get the message across in schools about what constitutes exploitation and when a "relationship" is exhibiting signs of becoming sinister or abusive.
Targeting the vulnerable
High-profile cases such as the Rochdale child grooming ring - for which nine men were jailed for a total of 77 years in May 2012 - and a frighteningly similar scandal in Oxford have at least meant that the issue is being raised in schools. "Girls are being targeted," says a principal of a secondary school in an area with many social problems. "They are charmed by snazzy cars with loud stereos, and the soft drugs and promise of presents. Unfortunately, it is often the most needy girls who are most susceptible."
Although the girls singled out tend to be from unstable families, or in the care of local authorities, this is not always the case. "The status symbol of the bad boy or older man has always been a thing for some girls," says another principal, of a hugely oversubscribed selective school in a wealthy area of London. "We recently had a devastating incident with a sixth-former who attempted suicide. It turned out that she had been made to perform sexual favours for her so-called boyfriend's friends since Year 9 (when she was 13-14). Her parents - one was a doctor, the other a teacher - had no idea."
To find out more about these relationships between young girls and predatory men, I speak to a group of girls whose school I am visiting. They are hanging around after school and, because teenagers are so loud, it is easy to glean that they are going to the house of "some guy" named Ray.
As I wander along with them, eating chips, I ask how old Ray is. After much guffawing and screeching, Taneesha, all gold jewellery and bravado, tells me that he is 29. I ask them how old they are. They are all 15, except May, who is 16. "What do you ladies do at Ray's house?" I ask. After much demurral, they admit to "smoking some weed, sometimes drinking, watching TV and listening to music".
"Are any of you going out with Ray?" I ask. More screeching - but it transpires that May is "seeing him".
"Does he ever have friends round?" I ask.
"Oh, yeah. All the time," Taneesha says. "It's a party house."
I choose my words carefully. "Do any of Ray's friends find it strange that he hangs out with schoolgirls?" I expect more screeching, but they all look slightly puzzled.
"Nah," May says. "They like it. They get to play the bad man, because we are younger than them." I want to find out what she means by "the bad man", but we've arrived at Ray's. The door opens instantly, although no one is immediately visible.
"Are you all going to be OK?" I ask the girls. They don't get to answer, because a shirtless man appears in the doorway, his skin covered in tattoos, his skinny hips barely holding up his tracksuit bottoms.
"What the fuck are you lot doing?" the man yells, not really sounding like a kindly benefactor. "Who the fuck is that?" he asks, gesturing at me.
"A reporter," the youngest-looking girl says, meekly, and they all file into the house.
Once they are inside, he glares at me: "Fuck off, you fucking nosey bitch, and get off my fucking property or I'll call the feds." He slams the rust-red door. Assuming that by "feds" he means police, I leave, not wanting to affront his law-abiding sensibilities.
A couple of days previously, I had received a worrying email from a girl I coached three years ago. Her parents had hired me in the vain hope that she might pass some exams after being expelled from school for drug possession. She came from a traditional Asian background, and now she had managed to be expelled from home as well, for promiscuity, stealing and more drug-taking. She is 17, and living with someone who a colleague told me is bad news. I arrange to meet her for coffee.
"Nah, it's wicked, Miss," Vanisha tells me, tearing the top off a sugar packet with her bright pink talons. "I never have to work: he buys me everything I want. I get my hair done every week and I can smoke weed all day. And do coke at weekends."
"What does this boyfriend do?" I ask.
Vanisha giggles. "Andre is an entrepreneur."
"I see," I say. "I assume you're having sex with him?"
She giggles again. "Of course I am."
"How old is he?"
Another giggle. "He's proper old. He's 36. But I like older men. They've got money."
I must look appalled because she shrieks at me. "Don't look like that! All my friends have an Andre. Look, if we put you in some better clothes and do something with your hair, you can come to his party tonight."
She leans in, conspiratorially. "But don't tell him you're a teacher or a writer or whatever. Tell him you're doing beauty and that you just broke up with your boyfriend. They'll be weird if you tell them you have a boyfriend. And definitely don't tell them your age."
I go to the party feeling morally and physically uncomfortable - the former for obvious reasons, the latter because I've hidden my phone in my knickers, Vanisha having advised me not to bring anything of value "because sometimes the guys borrow our money or check our phones".
Andre's house is a dilapidated terrace, the blaring music audible to the inhabitants of the nearby graveyard. The fug seeping from the building is enough to get the pigeons picking through the overflowing bin outside stoned. I am actually glad of the smoke and the dark - even these clothes wouldn't help me to pass as one of Vanisha's contemporaries in the light.
Inside, it's worse. At the parties I usually go to, men and women mingle, people laugh and dance. At this event, the two sexes sit in distinct groups on opposite sides of the room. The men gesture and talk loudly, but it's impossible to hear them over the music. The girls sit quietly, never seeming to relax or enjoy themselves. The age difference between the two groups is substantial - and painfully evident.
The girls smoke, but only when one of the men brings a joint over. Occasionally, one of the girls is summoned by their "man" and disappears. There is never any question of them not going to do whatever it is they are going to do. Other than that, there is no mingling.
Eventually, Andre wanders over and Vanisha all but clicks her heels and salutes. Once she has finished fawning over him, he clocks me. "Who's this?" he asks, looking me up and down in an utterly creepy way.
"I told you about her," Vanisha says. "She's my mate from beauty college. We're cheering her up. She just finished with her man." Andre makes an almost imperceptible noise and his lip curls in what might be a smile.
Vanisha, clearly relieved, whispers to me: "He's fine, isn't he?"
The girls fall back into chatting: make-up, beauty and celebrities seem to be their safe topics. I am itching to ask questions. Are they at school? Why are they here? Where are their parents? Is this as dodgy as it looks? But I realise that I could be inviting trouble.
I also realise that they are seriously wasted: Vanisha knocked back most of the vodka she bought in about 10 minutes, and they are all slurry and giggly. When another girl is summoned by her so-called boyfriend, she stumbles. "I told you not to get so fucked up," he hisses at her, before dragging her away in a not altogether loving fashion.
Eventually, Andre fetches Vanisha and she totters off with him to the kitchen. Left with the others, I admire the jacket on a blonde girl sitting next to me. "A present?" I ask. "Yeah," she says, unpleasantly. "You won't be getting one of these for a while." Two of her friends start to giggle and they all collapse into stoned, conspiratorial laughter.
Vanisha returns in time to rescue me. She looks really drunk, but together enough to seem worried. She takes me aside. "One of Andre's friends likes you. Really likes you."
"And?" I ask.
"Andre says that if you want to stay you have to go and chat to him upstairs."
She can't quite look me in the eye.
"What does 'chat to him' mean?" I ask.
She shrugs. "What are you going to do?"
"I think I should go," I tell her. She nods and looks relieved.
The walk to the door, which I try to make look like a casual amble, is one of the longest of my life. Outside, I run.
I spend the next few days speaking to as many girls as I can - girls from different backgrounds, living different lives. It would be wrong to suggest that a pimp or pusher lurks on every corner waiting to entrap our young women. But every girl I spoke to, from the most settled to the most troubled, had a story to tell, from their own life or from the lives of their friends. These stories covered the spectrum of abuse, from "friendly" offers of lifts from male strangers to the worst crimes men can commit against women.
The things that make teenage girls likeable - their endearing vanity, their urge to fit in, their needs to explore and rebel - are the very things that make them vulnerable.
The final group of girls that I meet attend a school near where I live. It is Saturday and they are in high spirits, getting ready for a party that night. The theme is "pimps and hos".
As the girls squeeze into basques and six-inch heels and layer on the make-up, I ask if they think that such a theme could be deemed inappropriate in light of the Rochdale case and the many women and girls suffering in the sex industry. They are nice young women - bright and thoughtful - and they all look slightly worried by the question. But their worry soon dissipates when the boys turn up in giant furs and carrying pimp canes (which an actual pimp could use to beat his workers).
"Come on, you bitches," booms a good-looking boy with a juvenile attempt at a beard, playfully swatting one of the girls on the backside. I can hear their high-pitched laughter and mock protesting over the clatter of their heels as I drive away.
*All names have been changed. Chloe Combi is a former teacher who writes about teachers and teaching.