Girl of 14 lives like a prisoner. Her crime? To be an asylum-seeker in Blunkett's Britain

Beriwan Ay shares a cramped room with her two younger sisters, her brother and mother. There are four single beds and a bunk bed but the walls are bare. Through a small window that opens only a fraction, all she can see is a high fence.

Beyond are steel gates and a perimeter wall topped with barbed wire. The guards at Dungavel detention centre near Glasgow allow her outside for two hours a day if they are in a good mood.

The 14-year-old has never committed a crime, but she is one of more than 50 children currently being held at detention centres for asylum-seekers in Britain. Thousands of children pass through such centres every year with some held for months at a time.

David Blunkett, the Home Secretary, argues that children such as Beriwan, who come to Britain to seek asylum, must be locked up, otherwise they would escape and live illegally in this country. However, leading campaigners say there is no evidence to support this claim.

The Ay family, Kurds who fled persecution by military police in Turkey, have been locked up in removal centres for nearly 10 months, and the psychological impact is already taking its toll. The children are believed to be the longest-serving children in detention centres.

"I don't sleep properly, I feel very tired all the time and I'm behind on my schoolwork because the books we use are for primary school children," said Beriwan, who wants to train as a lawyer. "My little sister is depressed and her hair is falling out. This place feels like a prison."

The Ay family – Beriwan, sisters Newroz and Medya, brother Dilowan, mother Yurdurgal and father Salih – left Turkey in 1988. They lived in Germany for 11 years but came to Britain after the German authorities threatened to send them back to Turkey. This happened to the father, who was deported to Germany last year.

For three years, the children attended a school in Kent, where their teacher Jane Cummins describes them as an "exceptional" family.

"They were all that you would want your own children to be," said Ms Cummins, a language support teacher.

This week, a petition containing 20,000 signatures from people protesting over the detention of children in Dungavel will be presented to the House of Commons. The Ay family's case will also be heard in the High Court.

Beriwan said she is scared of going back to Germany. "We came to England because we thought it was a democratic country," she says. "I have done nothing wrong, so why do they treat us like this?"