The Court of Appeal has overturned last year's finding by a High Court judge that Ofsted inspectors were wrong to penalise the mixed-sex Al-Hijrah school in Bordesley Green in Birmingham.
Margot Parker, UKIP's spokesperson for Women and Equalities, said: "Although the Court of Appeal ruled this school was discriminating against its pupils, there are still many questions to be answered.
"First of all I find it most concerning that the situation ever arose in the first place – there should have been checks and balances against segregating boys and girls.
"Secondly, I am astonished the High Court made a decision to clear the school of discrimination, leading to this appeal by Oftsed.
"Lastly, there is the very real concern this policy did did disadvantage girls more than boys. This was rejected by the Court of Appeal.
"This is Britain, this is 2017 – surely no-one considers this form of segregation, where boys and girls from Year Five are completely separated, even being made to walk in different corridors, is acceptable.
"Now let us tackle every single school which follows such backward policies, to make sure this does not happen again."
Gender segregation at Islamic School ruled unlawful / UKIP. Oct. 13, 2017