Ofsted chief inspector Amanda Spielman said in its annual report that almost half of Jewish independent schools - 47 per cent - were failing to meet the independent school standards.
If a school does not meet any of the independent school standards, then it cannot meet the overall required standard for management and leadership, the report stated.
Mrs Spielman once again called for stronger powers to inspect unregistered institutions, saying Ofsted was continuing to work “with one hand tied behind our back”.
She urged the Department for Education to act on commitments to tackle illegal schools “as soon as possible”.
The weak legal definition of a school was a “loophole that is exploited by the unscrupulous to operate out of reach of legislators, law enforcers and regulators,” she said.
“Even when those running illegal schools have been successfully prosecuted, there are no powers to close them down and some have continued to operate.”
Ofsted’s unregistered schools task force has investigated more than 600 settings in four years and found 290 cases of unregistered schools.
“We found safeguarding or health and safety concerns in over a third of them and issued warning notices to 83 that we believe are unregistered schools,” she said.
“Since these warnings, over 50 per cent of the unregistered schools visited have changed the way that they run to comply with the law. “They achieve this most commonly by reducing their hours to below 18 hours per week. Fourteen per cent have closed and 12 per cent have registered as independent schools.”
But legal constraints on collecting evidence “make this work much more difficult than it could be,” she said.
Hackney Council in London, which called in a report two years ago for the government to introduce new laws to crack down on unregistered institutions, believes there could be more than 30 local yeshivot that lie beyond the reach of the educational authorities.
Yeshivot argue they do not meet the current definition of a school and therefore are not subject to Ofsted scrutiny.
