A landmark legal battle has begun in the Court of Appeal over whether an Islamic faith school's policy of segregating boys from girls amounts to unlawful sex discrimination.
Demonstrators outside the Royal Courts of Justice carried banners saying "gender segregation is gender apartheid" as the first case of its kind got under way before three judges.
Ofsted chief inspector Amanda Spielman is challenging a High Court ruling in November last year that cleared Al-Hijrah school in Birmingham of operating an unlawful policy of segregating the sexes from year five.
Her lawyers argue the policy is unlawful and segregation leaves girls "unprepared for life in modern Britain".
Ofsted inspectors had penalised the mixed-sex school, which is maintained by Birmingham City Council, following a two-day June 2016 inspection which found that its policy constituted discrimination under the 2010 Equality Act.
Overruling the inspectors, Mr Justice Jay said they had taken an "erroneous" view on an issue "of considerable public importance".
He ruled: ''There is no evidence in this case that segregation particularly disadvantages women.''
The judge allowed Ofsted, the body that regulates schools in England, to publish the rest of a controversial inspection report placing the school into special measures because books found in the school library gave tacit approval to domestic violence.
Ofsted's chief inspector, who is in court in person, is appealing over the segregation ruling in a two-day hearing.
Helen Mountfield QC, representing Ofsted, asked the appeal judges to rule that Mr Justice Jay "erred in concluding the gender segregation observed in this school is not discriminatory".
Ms Mountfield argued the judge had taken the wrong approach and only considered whether girls attending Al-Hijrah were treated less favourably than boys "as a group".
"He didn't ask, as he should have done, whether individual pupils suffered particular detriment which pupils of the opposite sex would not suffer," said the QC.
If the correct approach had been followed the judge would have found "there is direct discrimination against individual girls at the school because a girl who wishes to socialise with a boy at school cannot and is treated less favourably than a boy who wishes to socialise with the same boy, and can".
Ms Mountfield said the same was true if a boy wanted to socialise and learn with a girl but could not - "each is suffering less favourable treatment because of their sex".
"If boys and girls in a school which is registered as a mixed-sex school lose the opportunity to work and socialise confidently with members of the opposite sex, as Ofsted says they should do, they will go into the world unprepared for life in modern Britain where they are expected to be able to work and socialise in mixed-sex environments."
But segregation was particularly detrimental to girls because females were "part of a group with the minority of power in society", said Ms Mountfield.
Women were at a psychological disadvantage because "in the workplace there are more powerful men than women".
Ms Mountfield said Al-Hijrah was an Islamic voluntary aided school which admits pupils of both sexes between the ages of four and 16.
From year five, however, boys and girls were completely segregated for all lessons, as well as break and lunchtimes and for school trips and all school clubs.
Following the June 2016 inspection, the school was deemed to be inadequate and requiring special measures.
After complaints from the school board, the inspection report was amended in August 2016 to acknowledge that segregation had not been commented on adversely in previous inspections.
Ms Mountfield submitted the fact that the less favourable treatment resulting from segregation had been overlooked in the past did not make it lawful.
She said: "The practical consequences of segregation for girls are more harmful than for boys."
There was "the necessary implication that females are intrinsically inferior to, or relatively different from males in day-to-day work and social contexts".
She said the latest inspection of Al-Hijrah was in June this year and it was once again placed in special measures.
An order had been made to turn it into an academy, which would involve a change of management.
Lawyers for the school's interim executive board said in a statement they were resisting the appeal, adding: "The board says, as the High Court judge found, that boys and girls are treated entirely equally at the school and there is no bar on separating boys and girls as it has done.
"It points out that Ofsted did not claim that separation was discrimination until 2016."