An investigation has uncovered potential cases of abuse and neglect at illegal schools across the country including a faith school in Westcliff.

More than 50 abuse or neglect cases have been uncovered in illegal faith schools in the last three years but no one has been prosecuted over them.

Pupils were being indoctrinated by extremists and exposed to danger in underground religious schools.

Many of the other schools were keeping children in filthy conditions, with no regard for health and safety law.

The BBC team filmed in a suspected unregistered ultra-orthodox Jewish school in Westcliff where they caught on camera a teacher appearing to hit a pupil’s head.

Anne Longfield, the Children’s Commissioner for England, told the BBC investigation the footage showed "huge safeguarding issues".

The synagogue, on whose grounds the school is based, said it was not aware of any incidents, but asked for more information.

Photographs from inside two other suspected unregistered schools show shocking conditions, including poor food hygiene, dangerous wiring and dirty rooms.

And in the case of a Birmingham Islamic school, material was discovered advocating killing gay people.

Of the unregistered schools where a religious ethos was known, half were Islamic.

An NSPCC spokesperson said: “These are very concerning findings. These schools could be employing staff who have not been subject to background checks or safeguarding training.

"Parents could have no idea these schools are illegal when choosing them so may be unaware of the potential risks they pose for their children.

"It’s vital that everyone who works with children undergoes full and rigorous checks to keep children safe.”

Ofsted said it has identified more than 350 illegal schools, and since 2014 has issued safeguarding alerts – concerns of abuse or neglect – regarding 50 of them.

However, despite the findings, the Department for Education has been unable to carry out prosecutions because of a loophole in the law.

Chief Inspector Amanda Spielman said the law was not ‘strong enough’ because it did not allow Ofsted to gather the evidence needed for a prosecution. ‘We can’t even pick up evidence that we find there,’ she told a BBC news investigation.

‘If we find unsuitable teaching material we can’t even take that away.’

Schools must register with the Government, but some small faith schools are refusing to do so because they do not want to comply with the national curriculum.

Parents are able to take pupils out of mainstream schooling by claiming they are being home-schooled – when really they are attending these secret institutions.

Ofsted has been hunting down these schools for several years amid fears some may be breeding grounds for religious extremism.

The Department for Education said: "The secretary of state has to consent to a prosecution. This happens at the end of the process. So far no case has reached that stage."