An investigation by the Office for Standards in Education, Children’s Services and Skills (Ofsted) has found that the United Kingdom is home to a host of unregistered, illegal schools, many of which are faith-based.

Sir Michael Wilshaw, the Chief Inspector of Schools and head of Ofsted, assembled a team of seven investigators to find and track illegal schools in Britain. The team found more than 100 such schools operating outside of Ofsted’s purview, with over half them being run as faith-based institutions.

Any school that offers at least 20 hours of instruction per week must register with Ofsted.

Roughly one-third of the faith-based schools were Muslim, with one-sixth being schools Jewish and one-sixth Christian.

Wilshaw wrote a letter to Education Secretary Nicky Morgan outlining his team’s findings and their concerns:

“What we have found so far is likely to represent only a small proportion of the illegal schools operating across the country. Inspectors are hearing about suspected new cases every week. I therefore remain extremely concerned about the number of children and young people attending these schools who may be at significant risk of harm and indoctrination.”

Areas rife with illegal schools included London, Birmingham, Luton, Wolverhampton and Stoke-on-Trent. Wilshaw told BBC Radio 4 that seven schools had over 400 pupils each.

Many of Ofsted’s concerns were practical, with several safety violations highlighted the letter. Investigators found that minimum safety standards such as clear fire exits and fire escapes were not met.

One school also had chemistry equipment, including chemicals for labs, in an unlocked cabinet in the same room where students ate their lunches.

Staff in unregistered schools were not subject to Ofsted’s background checks and certification processes, meaning that pupils’ safety may have been compromised.

Wilshaw said that curriculum in unregistered schools remains an Ofsted concern, with some schools including literature Wilshaw described as “homophobic.”

Ofsted has also suggested a link between a growing trend to educate students at home and the proliferation of unregistered schools. The government’s position indicates a suspicion that homeschooling is too often an excuse for enrolling students in faith-based schools that are weak on curriculum. The British Humanist Association (BHA), which has campaigned against faith-based schools, said in a call for the government to take swift action that:

“… on the same day that Sir Michael Wilshaw has called for tough action on illegal schools we have launched a new whistleblowing service for former and current pupils who have experienced indoctrination, misinformation, discrimination, neglect, and abuse in their schools.”

Ofsted and the Department for Education are raising concerns about both educational equity and quality. Wilshaw reinforced the government’s commitment to ensuring that every student be provided a high-quality education that is also in line with “British values” — a phrase increasingly used by the government and which generates questions over its exact interpretation. The Department and Ofsted have made clear that “tolerance and respect for others” are priorities.

The consequences for those who operate unregistered schools will be severe, Wilshaw states:

“Ofsted will support the DfE and Crown Prosecution Service (CPS) in taking forward prosecutions, by pursuing investigations into illegally operating schools vigorously and preparing strong cases against the individuals involved.”

In the letter, Wilshaw says that he is concerned that these 100+ schools represent just a fraction of the total number of unregistered schools operating in Britain.