A series of schools have torn up controversial sex education policies that appeared to advocate a return to lessons pandering to anti-gay prejudice.

The Independent disclosed that campaigners had identified more than 40 schools, including 19 of the Government's flagship academies, which had published policy statements echoing the language of Margaret Thatcher's notorious Section 28 legislation. The Department for Education (DfE) condemned their "unacceptable" statements and contacted the schools to investigate.

The two Crest Academies for boys and girls in Neasden, North-West London, said they would scrap a promise on their website not to allow the "promotion of homosexuality".

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A spokesman for the sponsors' academy, E-Act, described the use of the words as a "process oversight, which reflects neither the ethos nor the behaviour of the Crest Academies".

Tasker Milward School in Haverfordwest, Pembrokeshire, apologised for any distress caused by its failure to remove an "an old policy not in operation" from its website.

West Lakes Academy in Cumbria said its original sex education policy, which has since been abandoned, had been drafted by the Place Group, an organisation that advises schools on converting to academies.

A Place Group spokeswoman said it provided "template policies for schools", although governing bodies were responsible for their adoption. She said it had never been the company's intention to provide schools with outdated materials and was writing to clients to remind them to review policies to ensure they complied with current legislation.

Several other schools appeared to be rewriting their policies today as statements of their sex education guidelines were taken down from their websites.

The Welsh Government spokesman said it would contact all schools to reinforce their responsibility to teach youngsters "in a way that does not subject them to discrimination".

Tonight gay rights campaigners blamed the confusion on the DfE's failure to set out clear guidelines to schools on the content of sex education lessons.

Wes Steeting, head of education at Stonewall, said: "We need to see very clear guidance about the importance of tackling homophobic bullying and the promotion of a curriculum that is inclusive."

Benali Hamdache, the London Green Party co-ordinator, who has collected a 4,000-name petition protesting over the use of Section 28-style language by schools, said: "Sex and relationship education needs a dramatic rethink. The lack of national guidance means schools do not have clear responsibilities as to what they should be teaching."

Pavan Dhaliwal of the British Humanist Association, which identified the schools, said: “We welcome the Government’s investigation into this matter. These schools’ policies must urgently be updated and the schools must take steps to ensure no pupil is discriminated against because of their sexual orientation or gender identity.”

But she added: “We think a lot of the fault of this lies with the Government’s own sex and relationships education guidance.”