The sex-education policies of dozens of schools are to be urgently investigated by the Government after the institutions were accused of returning to the anti-gay prejudice of the 1980s.

Ministers, Opposition MPs and gay rights activists united to express anger and alarm over the disclosure that academies across the country had adopted policy statements that echoed the notorious Section 28 brought in by Margaret Thatcher 25 years ago.

The legislation, which was overturned by the Blair government, banned teachers in lessons from “intentionally promoting” homosexuality, a form of words that critics denounced for discriminating against gay pupils.

Download the new Independent Premium app Sharing the full story, not just the headlines

Campaigners have identified more than 40 schools across the country that stress in their sex-education guidelines that governors will not allow teachers to “promote” homosexuality, or are ambiguous on the issue.

The presence of many academies in the list will be an embarrassment to Michael Gove, the Education Secretary, who has championed them as a way of driving up standards.

A spokesman for the Department for Education (DfE) said tonight: “What these schools have done by singling out homosexuality is unacceptable.”

A source in the department said ministers were “concerned” by the revelations and had instructed officials to launch an immediate investigation. Many of the schools have adopted a wording for sex and relationship education policy guidelines suggested by independent companies which advise on the switch to academy status, The Independent understands.

But the sudden reappearance of language used under Section 28 provoked fury among gay rights activists.

The campaigner Peter Tatchell said: “This is spookily similar to Section 28 in Britain and the new anti-gay law in Russia. These schools are abusing their new freedoms to pressure teachers to teach gay issues in a way that will discourage them from saying anything positive that could be construed as ‘promotion’.”

Wes Streeting, head of education at the campaigning organisation Stonewall, said: “Given the deeply damaging effect that Section 28 had on the education and well-being of so many young people, it is alarming that some schools continue to have it enshrined in their policies.”

Inside Politics newsletter The latest news on Brexit, politics and beyond direct to your inbox Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive updates on politics every morning by email Update newsletter preferences

The British Humanist Association, which campaigns against faith education, said it had uncovered 44 schools that either replicated Section 28 or were “overly vague” on the issue.

“It is simply unacceptable that over a decade after the repeal of the pernicious Section 28 that these schools continue to enforce similar policies,” the association’s spokeswoman, Pavan Dhaliwal, said. “All of the schools identified must urgently review their sex and relationships education policies.”

Three academies run by the United Learning tell parents: “Staff are able to engage in objective discussions on homosexuality but not to promote it.” They are: Swindon Academy; Stockport Academy; and William Hulme’s Grammar School, Manchester.

A spokesman for United Learning said it was opposed to discrimination of any kind – and Swindon Academy had recently completed a major partnership project with Stonewall. He added: “We are now in contact with Stonewall to discuss their concerns and will of course amend the policy to avoid any misinterpretation in the future.”

Grace Academy, which runs schools with a Christian ethos in Coventry, Solihull and Darlaston in the West Midlands, says: “The governing body will not permit the promotion of homosexuality.” No one was available for comment last night. The two Crest Academies for boys and girls in Neasden, north-west London, say: “The Governing Body will not permit the promotion of homosexuality.” Calls to the schools were not answered.

Tasker Milward School in Haverfordwest, Pembrokeshire, reminds staff that they “shall not intentionally promote homosexuality or publish material which actively promotes homosexuality”. Calls to the school were not answered.

There are no national curriculum guidelines on sex education and the details of lessons are left to individual schools to draw up. However, schools are required to comply with the Equality Act, forbidding any discrimination.

Stephen Twigg, Labour’s shadow Education Secretary, said: “Michael Gove must intervene to ensure all schools obey their duties under the Equality Act. “It seems some schools, perhaps not knowingly, are still using guidance from before Labour’s repeal of Section 28.

“Labour got rid of Section 28 in 2003 to ensure schools taught about homosexuality in an open and honest way. Homophobic bullying is still too common, we must ensure we redouble our efforts to tackle such prejudice.”

Stephen Williams, a Liberal Democrat MP, said: “We need to get a grip on this to ensure schools aren’t breaching the guidelines that are in place to combat homophobic bullying.”

Graham Stuart, the Tory chairman of the Commons Education Committee, said: “It looks like an echo from the past. It looks as if schools have just copied that wording from years ago, before Section 28 was revoked, rather than with any deliberate intent.”

The DfE said: “All schools can draw up their own sex-education policy, but they must ensure they do not discriminate on grounds of sexual orientation. Our guidance makes it clear that schools should not promote any sexual orientation. The DfE will be looking into these schools.”

'Admin error’ and u-turn

In its first statement of its sex education policy, the Castle View Enterprise Academy in Sunderland could not have been clearer. It said: “The Governing Body will not permit the promotion of homosexuality.”

After being contacted by The Independent, it deleted the guidance from its website. The academy said the “incorrect information” was “one of several policy drafts shared by schools and project management companies as examples before the academy opened”. It said the policy had never been approved by its governing body. Principal Janet Bridges said: “We are thankful this administrative error has been brought to our attention and apologise for any upset it may have caused.”

An identical phrase was used by Colston’s Girls’ School, Bristol. And it executed a similar U-turn when contacted by the Liberal Democrat MP for Bristol West, Stephen Williams. He said: “I was amazed when I saw it and assumed at first it was some old policy from when it was a private school.”

Other schools are expected to rapidly delete similar guidance.

Nigel Morris