The safety and well-being of hundreds of children are being put at risk by their education in unregistered schools illegally operating in several parts of England, the chief inspector of schools has said.
Sir Michael Wilshaw revealed that three unregistered schools shut down by watchdog Ofsted in Birmingham last month were offering a narrow Islamic-based curriculum using anti-Semitic, homophobic and misogynistic material in conditions which represented a fire risk.
A total of 94 pupils were being taught by adults who had not been suitably checked or cleared to work with children, and conditions in one of the locations were described as "unhygienic and filthy".
Sir Michael was critical of "confusing and unhelpful" advice given by Department for Education officials to the owners of the properties where the unregistered schools were located, giving them the impression that they could carry on teaching while applying to be registered.
In a letter to Education Secretary Nicky Morgan, he warned: "This sends out an entirely wrong message of what the DFE perceives to be acceptable practice. Indeed, it could have the unintended consequence of encouraging others to open such schools."
Sir Michael called for an "urgent" review of DFE policies and procedures to ensure that illegal schools are disrupted and closed down, and that they are not able to use the process of registration as a cover for continuing to operate.
He asked Ms Morgan to agree that Ofsted should be the public body responsible for bringing prosecutions in cases of this kind.
Investigations are under way to support prosecutions in the case of the three Birmingham schools, where clear evidence was found that all three settings were operating as unregistered schools, said Sir Michael.
He reported "serious fire hazards, including a blocked fire escape and obstructed exits" and "inappropriate books and other texts including misogynistic, homophobic and anti-Semitic material".
In his letter, Sir Michael warned that the existence of illegal unregistered schools was "a serious and growing threat to the safety and well-being of hundreds of children in several English regions".
The Ofsted chief said: "I remain concerned that the number of children being educated in unregistered schools in parts of the country is far higher than is currently known by local authorities or the DfE.
"Ofsted's work to ensure that all maintained and independent schools promote British values is being seriously undermined by the growth of these settings."
Sir Michael last month asked Ms Morgan for Government support to ensure that Ofsted has the resources needed to identify and support the prosecution of illegally operating schools, and his letter welcomed the Education Secretary's "positive response" to his request.
A team of inspectors has been established to focus exclusively on identifying, investigating and supporting the prosecution of those operating unregistered schools, he said.
A DFE spokesman said: "Since 2010, we have taken robust steps to tackle unregistered schools and improve safeguarding and this includes being completely clear it is a criminal offence to operate an unregistered independent school.
"We agree with Ofsted that more needs to be done and will be strengthening our communications to potential providers.
"We are also introducing further powers to regulate settings which teach children intensively and to intervene and impose sanctions where there are safety or welfare concerns.
"We are pleased Ofsted has agreed to take forward these prosecutions and we look forward to immediate progress."
Shadow education secretary Lucy Powell said: "That this Government appears to be content to allow children to remain in illegal schools where they are at risk of exposure to narrow curriculums, misogynist, homophobic and anti-Semitic material and staff who haven't been cleared to work with children, is truly shocking.
"Every day children remain in such a school is a day too long. The Government has a basic responsibility to ensure that children are kept safe, and yet despite warning after warning, they have failed to take swift action and arrangements for closing down unregistered schools are still wholly inadequate. This is nothing short of a disgrace.
"The consequences of the Government failing to take this issue seriously are severe - significant numbers of children, including those who could be at risk of being radicalised, are ending up in unregistered provision, where they could be exposed to extremist ideologies. Without a doubt, the dangerous void in the local oversight of our schools system, created by this Government's education policy, is allowing children to end up in harm's way."
Sir Michael told BBC Radio 4's PM programme: "These schools are not registered with the DfE. Therefore they are not regulated and inspected by Ofsted.
"We are finding many more of these places opening up across the country. Our inspectors are going into some of these institutions and seeing the most terrible conditions.
"We are seeing open drains, we are seeing absolutely filthy conditions, we are seeing staff who are unchecked and unvetted and the most appalling literature - homophobic literature, misogynistic literature, anti-Semitic literature - in these places.
"Children are at risk in these places and I think unless something is done to stem the increase of this unregistered provision we will see youngsters really, really, really at risk in our country of being abused and radicalised.
"We believe there are many more. We are forming a taskforce for Ofsted ... who will investigate unregistered provision, go into areas where we think these places exist and we will take the necessary action to close them and then to prosecute the proprietors of these places."
Sir Michael said prosecutions for operating illegal schools were "long overdue".
"Once we start prosecuting people for running these institutions and breaking the law then fewer people will do this sort of thing and run this sort of operation," he said.
Independent schools offering full-time education in England must register with the DFE and accept inspection by Ofsted.
They are required to meet standards on education quality; the spiritual, moral, social and cultural development of students; welfare, health and safety; suitability of staff, premises and accommodation; and leadership and management of the school.
Failure to register a school attracts a maximum six-month jail sentence and £5,000 fine.
Rafique Patel of the Association of Muslim Schools said that growing numbers of "disillusioned" Muslim parents - as well as some from the Jewish and Hindu communities - were putting their children in independent schools because they were not getting the faith-based education they wanted in the state sector.
Mr Patel told PM: "It's obviously a very big concern that there is such a large percentage of parents who are disillusioned with the state sector and are moving towards these independent schools.
"Clearly, it is an issue if there are schools that should be registered which are not registered and maybe the Education Secretary should go out into these communities to find out what it is, educate them that if you do want to operate these schools then they have to be registered.
"Clearly, they are shooting up all over the place."
Mr Patel said schools using materials which are against the law "should not be operating in the sector". But he added: "To shut down a school because its drains are not working, or this or that, then puts 100 or so parents without their children having education the next day, and that's not the way to go forward."
He added: "I think the attraction of these establishments is the faith-based criteria which they want more of and they may not be getting in the state sector. I think the word 'narrow' is probably not the right word to use - I think the word is 'faith'."