Campaigners have accused the government of allowing a faith school to circumvent laws on gender segregation by converting into two single-sex schools.
Hasmonean High School, an Orthodox Jewish secondary school in Barnet, faced criticism from charity Humanists UK over teaching different aspects of the curriculum on the basis of gender.
Exclusive: Faith schools 'one of Britain's biggest problems'
Read: Hinds calls for more faith schools to become academies
Q&A: Do ministers really want new faith schools?
Since 2017, schools have been told to abide by new laws on segregation following the Court of Appeal's support for Ofsted in ruling against the Al Hijrah Islamic school, in Birmingham, which segregated boys from girls not only in lessons but at break time, and in school clubs and trips.
Hasmonean High School said it was for legal reasons that it applied to the DfE for permission to "de-amalgamate."
It said it has now been given the go-ahead, subject to the completion of documents, to split into two single-sex schools.
But Humanists UK has highlighted the school's website, which says boys and girls are taught different curriculums in Jewish and religious studies.
Director of public affairs and policy Richy Thompson said the school was teaching "sex-discriminatory curriculums."
He said: "It is shameful that the government has permitted a state school to circumvent criticism over its gender segregation in this way. The school no doubt believes it has got off scot-free through this loophole – but it shouldn’t be allowed to.
"The school’s new approach still should not be acceptable as it is still teaching boys and girls sex-discriminatory curriculums. That should be unlawful regardless of whether the school is mixed or single-sex. It is also very unlikely that the school will be upholding its duty to prepare children for life in modern Britain if it continues teaching a narrow curriculum."
As reported in Tes in February, the Yesoiday Hatorah School, a Jewish state primary school in Manchester, was also planning to split itself into two single-sex schools rather than integrate its pupils – following criticism by Ofsted for unlawful gender segregation.
And last month the DfE admitted it didn’t know how many schools illegally segregate pupils by gender.
Meanwhile, Hasmonean parents were said to have been told about the split in a letter sent out last week.
The school's executive headteacher and chair of governors said in a joint statement: “The proposal to de-amalgamate was made to place the academy on a more secure legal footing and ensure compliance with equalities legislation following advice from the Department for Education in the light of a court ruling regarding the operation of co-educational schools.
“A consultation took place from 25th January 2018 until 30th March 2018 on these proposed changes. In the view of the consultation responses, trustees did not identify any good reasons to not proceed with the proposal and submitted its application to de-amalgamate to the DfE.
A spokesperson for the DfE said: “Any school not complying with the ruling set out by the Al-Hijrah judgement should make the necessary changes as quickly as possible - that can include splitting into two separate schools.
“All schools must comply with the law and are subject to independent inspection to ensure they are doing so, while also delivering a broad curriculum for their pupils.”