A successful English independent Christian school is facing threats of being downgraded and even closure for failing to invite leaders from other religions, such as an imam, to speak in school assemblies.

The report came from the Christian Institute, which is giving legal support to the small school.

The Christian Institute wrote to Education Secretary Nicky Morgan saying the school's rating would be changed from "good" to "adequate" by inspectors for the regulatory group Ofsted.

The school is breaking new rules designed to promote "British values" such as individual liberty and tolerance, said a report in the Telegraph on October 21.

The rules were implemented following the Islamist "Trojan Horse" scandal, in which hardline Muslim groups attempted to "Islamize" State schools in Birmingham and impose an "intolerant Islamic ethos."

The Christian Institute said it feared that religious schools which are running against standards intended to fight extremism will have "disturbing consequences."

"Worryingly, evidence is already emerging of how the new regulations are requiring Ofsted inspection teams to behave in ways which do not respect the religious ethos of faith schools," Christian Institute deputy director Simon Calvert, wrote to Morgan.

"The new requirements are infringing the rights of children, parents, teachers and schools to hold and practice their religious beliefs," said Calvert.

He said his group was currently working with an independent Christian school, which has been marked down by Ofsted "for not promoting other faiths."

He added that the school was instructed that it should invite representatives of other faith groups to lead assemblies and lessons, such as an imam.

"While we obviously support attempts to address the problem of radicalization, the current regulations fail to do this," added Calvert.

Ofsted inspectors have warned the school it would undergo a further full inspection, which could ultimately lead to its closure, unless it could show how it was going to meet the new requirements, reported the Daily Mail newspaper.

The unidentified school was among 40 educational institutions across the country that had snap inspections in September following findings that Islamists had imposed strict religious practices in State schools in Birmingham.

The report also quoted a spokesperson of the Department of Education as saying that its standards for independent schools have been designed to ensure Britain's youth are well prepared for "life in modern Britain."