Leicester’s state Islamic school has been told its admissions criteria are “unlawful” because they discriminate against a Muslim group.
The Schools Adjudicator ruled that it was wrong Madani High gave Sunni Muslims priority over Shias.
The school’s policy also breaks the Sex Discrimination Act by turning away pupils to create the same number of boys and girls.
It is the second time in two years the Evington Valley Road school has been judged to have an unlawful admissions policy.
The adjudicator said it was possible Madani – which has dropped its commitment to having 10% non-Muslim pupils – would not have been approved if people thought it favoured one denomination.
The school’s admissions policy says priority is given to Muslim children, and defines “Muslim” as four named groups , which are all Sunni.
Chairman of governors Hussein Suleman said there was never any intention to exclude any Muslim group, and the school was already consulting on a revised admissions policy.
“This is creating divisions which don’t exist,” he said.
He said the school would comply with the ruling “without compromising our philosophy”.
The investigation followed a complaint understood to have come from a Shia who believed the policy was discriminatory.
Sunnis and Shias are the two main sub-groups of Islam and differ in some beliefs and practices. Sunnis make up 85% of the global Muslim population.
Coun Suleman said there were Shias at Madani, and at the school’s private primary, but he said he did not know whether any had been accepted at Madani since it became a state school.
Madani is allowed to give priority to Muslim children, just as Catholic schools give priority to Catholic pupils.
It was told to define “Muslim” when a complaint against its admissions criteria was upheld in 2008.
Coun Suleman said the school decided on its definition because it was the same as that contained in the deeds of the private Leicester Islamic Academy, Madani’s predecessor, written 20 years ago.
But adjudicator Dr Elizabeth Passmore said she could not “find a document currently applying to the school that designates it as being for a particular group of Muslims”.
She wrote: “It seems to me the school was expected to be a Muslim faith school, equally accessible to all Muslims.”
Madani must alter its admissions for September 2011. Leicester City Council said it would help the school.