A penal reform charity representing a teenage boy in a legal action against his "prolonged solitary confinement" in detention is to seek an appeal against a ruling that his conditions did not breach human rights laws prohibiting "inhuman or degrading treatment or punishment".
A High Court judge granted the 16-year-old a declaration on Tuesday that his Article 8 rights - the right to private and family life - were breached at Feltham Young Offender Institution in west London.
But Mr Justice Ouseley rejected a claim that his treatment amounted to a breach of Article 3 of the European Convention on Human Rights (ECHR) which states that no-one should be subjected to torture or to inhuman or degrading treatment or punishment.
The Howard League for Penal Reform, which brought the case on behalf of the boy, who cannot be named for legal reasons and is referred to as AB, said he had been "isolated in his cell for months on end", and provided with "only very limited access to education".
Chief executive Frances Crook said: "This is an important judgment. The court has declared this boy's isolation for certain periods and the denial of adequate education unlawful because it was against prison rules.
"It is disappointing that the court stopped short of accepting that keeping AB in isolation for over 22 hours a day was degrading and inhuman treatment. We will be seeking to appeal this part of the ruling."
The judge, sitting in London, announced that young offender institution rules on both "removal from association" - which relates to being kept in a cell and not allowed to mix with others - and education were breached.
He said: "I shall make a declaration that Article 8 was breached because the interference with his rights was not in accordance with the law."
At a recent hearing the judge was told that the boy, who suffers from "significant" mental health problems and whose behaviour is described as "challenging", remained in conditions amounting to solitary confinement for "almost the entirety of his time" at Feltham after being detained in December last year.
A QC for the Justice Secretary said it was accepted there had been "procedural errors" in the boy's case, which were regretted. A breach of Article 3 was denied.
The judge said that in the light of the concession that there had been breaches of the rules, and "the remedial measures being put in place to ensure compliance with the procedural requirements for removal from association and the provision of education", the main issue was whether Article 3 was breached.
Dismissing that part of the boy's challenge, he said that "there has at all times been a considered and proper justification for the removal from association" - initially to "protect officers, then to protect officers from AB and AB from inmates whose anger he aroused by shouting abuse..."
A Ministry of Justice spokeswoman said: "The safety and welfare of young people held in custody is our highest priority. We are grateful for the judge's findings and will consider these carefully.
"We are pleased that the judgment found there has, at all times, been a considered and proper justification for segregation in this case.
"Proportionate and justified segregation is an essential tool to manage offenders who would otherwise pose a significant risk to staff and other prisoners."