A Muslim free school accused of enforcing hardline Islamic practice has closed on the first day of an Ofsted inspection.
Following the sudden announcement, Michael Gove's free school revolution was branded a "minefield" by secular campaigners, who said the system was being "exploited" by religious groups.
The primary and secondary Al-Madinah school in Derby said it had closed because of "a health and safety issue".
The Department for Education said it too was investigating the school, which opened in September 2012 under the government's flagship free schools policy.
According to the BBC, Ofsted's findings were "so damning" the school was closed immediately.
It follows claims by teaching unions that staff were forced to sign new contracts forcing them to wear hijabs and female pupils were being told to sit at the back of the class.
The Derby Telegraph also reported concerns that staff were not allowed to wear jewellery and that only halal food was being served.
The schools regulator began a two-day visit to Al-Madinah in Derby on Tuesday.
Acting head teacher Stuart Wilson said the school would close temporarily.
Writing on the school website, he said: "Owing to a health and safety issue, I have taken the decision to close the school to primary and secondary pupils until I am confident that all children are safe on site.
"As parents, you will be informed directly, and on the website, when you are able to send your children back to school. I expect this to be in the very near future.
"Assuring you that we have your children's best interests at heart."
Terry Sanderson, president of the National Secular Society, said: "If half of the stories that have been appearing in the press are true, schools like Al-Madinah have no place in the British education system.
"If it has fallen under the control of people who have an agenda that does not accord with the values of the British education system, then they should be removed immediately and replaced by those with a more balanced approach."
He added: "The freedom these schools have is being exploited and abused by some religious groups and we suspect there are many that are not honouring the agreement they made when they were first approved. Using schools for proselytising and evangelism became much easier with the free school system."
A Department for Education spokesman said: "We were already investigating this school before allegations became public.
"We discussed the problems with Ofsted and it launched an immediate inspection. We are waiting for Ofsted's final report and considering all legal options."
The free school was opened in September 2012.
On its website, it describes "a strong Muslim ethos" with shorter holidays and longer school days "to maximise opportunities for pupil achievement and success".
It adds: "At the centre of our school is a community of pupils, able to enjoy learning in a caring Islamic environment which promotes a culture of high expectations and outstanding performance."