"Looking back, I think they were using me to make themselves feel better."

Kiri Joliffe, now 19, suffered years of bullying at school from a group of girls she called friends.

"One minute they liked you, the next they didn't."

But when she complained, her teachers wouldn't take her seriously.

It peaked when she was about 13, she says. But it never really let up for the whole time she was at school - and it centred on the way she looked.

"I had to have dental surgery which left my face very swollen, and then I had train tracks on my teeth.

"I also had big, dark bushy hair. I was a bit chubby and wore glasses.

"I used to get called Ugly Betty.

"Nothing about me was accepted. It was a very scary place."

'Manipulation and destruction'

With Anti-Bullying week under way, newly-published research identifies friendship bullying as more harmful than physical, verbal or cyber-bullying.

The study, by University of Hertfordshire researchers and published by the Journal of School Health, describes it as a particular form of bullying which causes harm to the victim through "the systematic manipulation and destruction of their peer relationships and social status".

Typically, the tactics of friendship bullies include "threatening to retract friendships, spreading rumours, purposefully ignoring and excluding the victim or using friendship as a bartering tool".

Lead author Kayleigh Chester says responses from a representative group of more than 5,000 young teenagers from across England suggest about five young people in every secondary class will have been bullied by friends in the past couple of months.

This type of bullying had a greater association with poor health and wellbeing among victims than any other form of victimisation.

According to Kiri, one girl in the friendship group was particularly powerful.

"She was really pretty, almost like a celebrity in the school.

"She wouldn't have to say a single word but if she stood up we would all follow her."

'It was torture'

It was this girl who dictated who was in favour and who was not, says Kiri.

More often than not, Kiri found herself out of favour - and even the teachers were sucked in.

There were untrue stories spread on Blackberry Messenger.

One rumour, that she had lice, resulted in a teacher insisting on checking her hair.

"It was torture," says Kiri.

"The bullying was an everyday thing and although I did pluck up the courage to talk to some of the teachers at school, there was no support and I felt as though nothing I was reporting was taken seriously.

"I forever felt let down."

Even in the sixth form "girls would give me the evils from across the room and boys would make sly comments".

Too often, teachers, parents and students fail to recognise deliberate social exclusion as bullying, say the researchers.

"It can be really difficult to identify and it is difficult to distinguish from normal conflicts within peer groups, so parents and teachers can be less likely to intervene to help victims," says lead researcher Ms Chester.

She wants bullying by friends to be acknowledged in school policies as a distinct form of the problem which warrants a specific prevention and reduction strategy.

"I think it really needs to be given as much attention as other forms of bullying, because acknowledging how harmful it is will help in intervening.

"It's really obvious it's a really damaging form of behaviour."

Image copyright NCB Image caption Kiri now volunteers with the Anti-Bullying Alliance

In the end Kiri solved her problem by quitting school and starting a BTEC at her local college.

There she became more self-reliant, made some real friends, decided on a career path and found a boyfriend.

She is now in the second year of a degree in criminology and law, volunteers with the Anti-Bullying Alliance and the National Children's Bureau and wants to be a barrister.

But she says the victimisation she suffered at school has had a lasting effect.

"I still suffer with feeling alone and trapped.

"I constantly worry about my appearance too and I always wonder if anyone is talking about me.

"It's very dangerous when a bully feels as though they have a lot of power, especially, as with my experience, adults empower the younger people in a negative way."