We're locking up more under 18s than ever before, and more than any other country in Europe. The Northern Echo has been given unprecedented access to a secure unit for young people, and in the first of a series of reports, Nick Morrison looks at how children end up in custody.

HOLLY doesn't remember much about that night. By her own admission, she was wrecked, "on everything", out of her head. What she does remember is that she ended up fighting with her mother's boyfriend and hitting him on the head with a glass ashtray. Then she went back to her mum's house and carried on drinking.

The next morning, she awoke to find the house surrounded by police, but it still didn't dawn on her how much trouble she was in. It was only when she spoke to her solicitor that it dawned on her. "He said 'You won't be getting out for this one'," she recalls. She doesn't remember how badly her victim was injured, but it must have been pretty bad because she was convicted of aggravated GBH and sentenced to four-and-a-half years in custody.

Now 16, Holly has served two years of her sentence, making her the longest serving resident at Aycliffe Secure Unit, which takes children aged 12 to 18 from all over the country. She has another two-and-a-half months to go.

She attacked her mum's boyfriend because he had given her mum a black eye. When she first arrived at Aycliffe, she was convinced he deserved it and she'd been badly treated. Two years on, she's had time to think again and change her mind.

"The first few months I was not bothered, I didn't care. Now I think I shouldn't have done it. Now I think I deserve my sentence; I shouldn't have gone and did what I did to him. Some days I think it was harsh on me, the slow days, but it was probably the right sentence for what I did," she says.

Holly, who comes from Lancashire, had been in trouble before: fighting, petty vandalism, getting in stolen cars, culminating in serving two months for assault. But that wasn't the start of the journey which has led her to Aycliffe. Nor was the day she was put in a children's home, at the age of 11. The truth is there probably wasn't one event which condemned her to spend a large chunk of her adolescence locked up: it was more the result of being brought up by a mother who used drugs and was unable to cope with her children.

'I had already started missing out on school, and I started going smoking with my mates. We were heading that way for quite a bit," she admits. "I got put in these kids' homes, then my brother came in and we got moved to this other kids' home. I was always arguing and kicking off with the staff and barricading doors."

Her story is typical of many of the children at Aycliffe, says secure unit manager Gill Palin. Although the individual circumstances are always different, there are enough common threads to present a convincing argument that it is their environment and upbringing which has driven them to offend.

She says: "These children have committed offences, some of them really horrific, but let's not lose sight of why they have done that, and 90 per cent plus have been either emotionally, sexually or physically abused. Because of their life experiences, they end up doing something.

"For every child it is different - some might have had good parents, some might not; some might have been using drugs, some might not; some might have been under a great deal of peer pressure to do things, some might not."

She says many of the children at Aycliffe have mental health problems, and the majority have suffered significant loss, whether through divorce or the death of a parent. Of course, this does not mean that any child whose parents divorce will turn to crime, but it can make them more vulnerable, particularly if other risk factors, such as peer pressure, are present.

"I don't believe any child is born bad or born naughty. Their life experiences and the way they're treated in society make them bad or naughty."

It's disturbing, although maybe not surprising given their backgrounds, that some of the young people prefer being at Aycliffe than being what they call "on the out". It's generally a relaxed atmosphere, and in many respects is similar to a children's home. The difference is that all the doors are unlocked in front of you and locked behind you. "Some kids say it is the best time of their life in here. What does that say about what it is like for them outside?" says Gill.

Holly can't wait to get out of Aycliffe, but it has given her stability for the first time in her life. In fact, it gave her so much stability, it was almost unsettling.

"This is the longest I've ever been in one place. When I first came here I used to move bedrooms, just to feel different. I have been in nearly every room in the house," she says. But it doesn't make her want to stay.

'I think I'm just going to go to a club when I get out, have a big party for a week. The day I walk out the gates I will be buzzing, but it will feel dead weird. I hate it here, I just want to get out.

"You just have to get on with it in here. You wake up and think 'One less day to go'. I put my calendar up on the day I got sentenced, marking off the days, but I got sick after a year and took it down. I can't believe these two years - what a waste."

It may have been a waste, but two years in Aycliffe, plus the group work which is an integral part of every inmate's time there, encouraging them to look at why they offended in the first place and what effects their crimes had, have given her time to think about where her life was heading.

"I never used to have a conscience. I never used to feel guilty, but I feel horrible and I feel sorry for the guy because of what we did. In here you have to think about things. You see what you do to people. If I say something to someone and they're upset, I see them everyday and see their reaction and I feel bad. It is going to be different when I get out. This place changes you, it makes you feel differently. I used to blame my mum. I still do in a way. If it was not for being put in kids' homes or having a normal bring up, maybe I would not be here. In a way, I do blame her, but in other ways I can't, because I did it. I have got myself to blame. I should have been more clever," she says.

Her relationship with her mother has also improved: "When I was out I didn't even talk to her. I hated her, but when I came here I started getting on with her. She went in detox, sorted her head out, and I get on better with her now than I've ever done. I think it's because we're far apart and it has brought us closer," she says.

She's not sure about returning to Rochdale. It's where her friends are, but she's honest enough to admit that the temptation to fall back into her old ways may be too strong.

"People say are you going to get in trouble again, and you say no, but when you think about it you can't say that. I'm going to try - try and get a job, see if I can get a nice little flat. If you have got that, you don't want to be coming in here again."

* "This is no holiday camp" - read The Northern Echo next Monday