Child asylum seekers are suffering abuse due to the Home Office and local authorities wrongly classifying them as adults, the Guardian has learned.

Evidence of children being physically attacked, neglected or abandoned when wrongly treated as adults, puts further pressure on the Home Office after a court of appeal ruling last week found the department’s assessment policy to determine the age of young asylum seekers was unlawful. The Home Office has been ordered to scrap the policy and devise a new one.

Laura Gibbons, a solicitor at Greater Manchester Immigration Aid Unit, has challenged children wrongly assessed as adults through the courts many times. She said that of 67 people the unit had worked with since July 2017 more than half – 36 – had been age disputed. Of these cases, 93% have been successfully challenged, the majority using legal action. Research by the unit found that one 14-year-old child was wrongly assessed as 22.

The Refugee Council also works with this group of children. Between July and September last year they dealt with 92 new cases of young people assessed as adults. Of these, 41 have been found to be children with 45 cases still ongoing.

Gibbons warned: “This is a safeguarding disaster in the making.”

One child who was accommodated with adults said: “I was bullied and my bed was slept in by adults. I was forced to sleep on the floor in the same room as the adult. I was under constant threat from this adult. He would grab me by the neck and push me around all the time.”

Other children reported:

being particularly scared at night when forced to sleep alone

being denied education

they were unable to manage things such as shopping, cooking and doctors’ appointments by themselves

they sometimes cried themselves to sleep

Unaccompanied child asylum seekers often arrive in the UK without identification documents. There is no foolproof scientific test to determine the age of a child or young person. Best practice is for professionals to carry out an age assessment over a period of time.

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Child asylum seekers receive more support than adults and cannot be forcibly removed from the UK until they have turned 18. However, there are cost implications for local authorities and both the Home Office and some local authorities have been accused of “exporting’” these children to the north of England having assessed them as adults simply by looking at them. Many who arrived in the south-east of England end up in a Home Office initial accommodation unit in Liverpool, others are wrongly locked up in adult detention centres.

One child asylum seeker who arrived in the UK at the age of 16 after a traumatic journey from his country where he was facing persecution, told the Guardian a Home Office official assessed him in a few moments by looking at him and added almost six years to his age, informing him that he was 21 rather than 16.

“There were a few other child asylum seekers at the police station claiming asylum like me. We told the woman from the Home Office our ages but she wrote down that all of us were born in 1995 making us 21. I was born in August 2001. I felt powerless. I was in a strange country where I didn’t speak the language. When I realised that my age could affect my immigration status I was very worried. If the Home Office or local authorities make a false decision on children’s ages they are playing with their lives and their futures.”

The boy, now 17, subsequently had his real age accepted and has been granted refugee status.

In the court of appeal case lawyers for an asylum seeker from Eritrea, known as BF, argued assessing someone’s age based on their appearance or demeanour is “inherently unreliable” and therefore unlawful.

Before the appeal, the Home Office amended its guidance, which now requires that two members of staff “have separately assessed that the individual is an adult” on the basis of their physical appearance and manner.

In ordering the guidance to be revised, the judge stated that the term “significantly over 18” was not sufficiently precise as to avoid huge differences in how it was applied, giving rise to the risk that children would be wrongly deemed adults and treated as such in the asylum system.

Gibbons said GMIAU’s research had identified many disturbing cases: “One young person dispersed into adult accommodation said adults there told him to stop crying at night because he is keeping them all awake.” She added that age assessments should not be carried out routinely but when they were deemed necessary should ensure “the child is properly supported by a trusted, independent adult so that the process is careful, holistic and keeps the child’s best interests at the fore”.

A Home Office spokeswoman said: “We are disappointed by the judgment and are considering its implications carefully. The Home Office and our accommodation providers take complaints extremely seriously. We have implemented changes to provide assurance that customer vulnerabilities are captured and understood, set up a regular safeguarding working group with senior staff from each of our providers and are reviewing our procedures around safeguarding to ensure these are fully aligned and represent best practice.”