A prestigious Catholic school in London fears that altering its admissions criteria – as it was ordered to do by an English government agency following a complaint from the British Humanist Association – will damage its Christian identity.

The London Oratory School came under review by the Office of the Schools Adjudicator (OSA) after a complaint from the British Humanist Association said its faith-based admissions policy unfairly favored Catholics over other prospective students, and less well-off Catholics.

The OSA helps clarify the legal position on admissions policies in schools in England, and its members are appointed by the Secretary of State for Education.

The state-funded school has responded to the OSA by appealing the High Court for a judicial review, arguing that the ruling threatens their "strongly Catholic ethos."

Representing the school is Charles Béar, who said, "the school view is that altering the faith-based criteria will alter the composition of the (pupil) intake and damage the school ethos."

He added that the adjudicator's investigation is badly flawed and misinterpreted the school's admissions policy to reach "logically unsustainable" findings, The Guardian reported.

He said the most concerning accusation from the report was that less wealthy Catholic families were "unfairly disadvantaged" by the admission criteria.

Bear said the school's strong Catholic ethos seeks to serve children from all over London, not just wealthy areas.

Because of its high academic standards, the school is a highly sought-after choice of school, with at least 800 prospective students applying for only 160 spots each year.

The school changed its 2015 admissions policies in response to the adjudicator's findings, but aims to receive clarification in hopes of changing it back in time for its September 2016 school year.

The school was founded in 1863 by the Fathers of the Oratory and aims "to develop young men and women of faith, good character, strong intellect and generous spirit" and "at all times the school serves as a witness to the Catholic faith," according to its website. The secondary school admits boys aged 7-18, and girls aged 16-18.

Students include the children of former prime minister Tony Blair, deputy prime minister Nick Clegg, and member of parliament Harriet Harman.