JFS has been downgraded from an “outstanding” school to a “school that requires improvement”, following an unannounced Ofsted inspection two months ago.

In a letter sent to parents today, the school’s chair of governors Michael Glass said that governors and senior teachers were “profoundly disappointed”, after falling by two whole grades in its Ofsted rating – from grade one to grade three out of four.

Mr Glass said: “in reaching its conclusions, Ofsted has given disproportionate emphasis to issues which do not go to the heart and soul of the school and has not portrayed accurately the school or given appropriate weight to the rich and varied educational experiences provided for our students”.

The spot inspection occurred in early July, after Ofsted said it had received complaints – although it would not elaborate further.

In its letter, the school said: “We have tried to obtain a better understanding of the complaints that triggered the Inspection but we have not been provided with details.

“We have however drawn a number of our own conclusions about the nature of the complaints from some of the comments which Ofsted have made in their report.”

When it was last inspected in 2009, JFS was judged “outstanding” in all categories.

The largest Jewish school in Europe with more than 2,000 students, it continues to perform well academically and had a record 16 Oxbridge offers this summer.

A separate question and answer sheet attached to the letter to parents suggested that Ofsted had concern over the school’s discipline policy and attendance record of some students.

But Mr Glass said in his letter that the inspection service had not taken account of the high volume of parents who responded to the Ofsted survey.

He said: “Despite Ofsted’s concerns about behaviour and safety, the parents’ survey showed that 99 per cent of parents said their child feels safe at JFS and 96 per cent of parents said the school makes sure its pupils are well behaved.”

He added that this year’s GCSE and A level results had been unavailable to Ofsted inspectors in July and were not taken into account when preparing its report.

The school made clear that the new Ofsted grading would not affect its funding.

JFS president Lord Levy responded by pledging his “full support and commitment” to the school.