Dozens of British schools have been accused of having homophobic sex education policies in line with the notorious 'section 28' of years gone by.
Campaigners said it was "simply unacceptable" that more than 10 years after the act was banned, it was apparently being replicated in more than 40 schools.
Section 28, which stopped councils ''promoting'' homosexuality, was the subject of protests from the moment it was introduced under Margaret Thatcher in 1988.
It was finally repealed by Tony Blair in 2003, and David Cameron apologised for it after becoming Tory leader.
The British Humanist Association (BHA) said it had found that "45 schools continue to have sex and relationships education (SRE) policies that either replicate Section 28 of the Local Government Act 1988 or are unhelpfully vague on the issue".
A Department for Education (DfE) spokeswoman said the claims were "unacceptable" and it would be looking into the schools.
The BHA said it believed 20 of the schools had policies that were "clearly offensive" while a further 22 seemed to imply that Section 28 might still in some way be in force. The other three were otherwise vague, it said. Eighteen out of the 45 schools are academies.
The charity said it believes that all the schools concerned should urgently review their policies to remove offending statements.
It carried out the research after being tipped off that Colston's Girls' School in Bristol's policy of its governing body does not permit the promotion of homosexuality.
A spokeswoman for the independent school said today: "The policy was immediately withdrawn and a replacement is currently being prepared which will be published on the school website in due course.
"The school is committed to creating an environment that promotes equality and respects and celebrates the diversity of all members of the school community."
BHA head of public affairs Pavan Dhaliwal said: "It is simply unacceptable that over a decade after the repeal of the pernicious Section 28 that these schools continue to enforce similar policies, while others have statements which are overly vague on this matter.
"All of the schools identified must urgently review their sex and relationships education policies to ensure that all pupils, whatever their sexual orientation or gender identity, are treated with equal respect and understanding and that homophobic and transphobic bullying is stamped out."
David Cameron apologised for the Conservatives' stance on Section 28 after becoming Tory leader. It was devised to deal with concerns over homosexual content in sex education lessons in schools, but was condemned by campaigners as discriminatory.
The DfE spokeswoman said: "What these schools have done by singling out homosexuality is unacceptable.
"All schools can draw up their own sex education policy but they must ensure they do not discriminate unfairly on grounds of sexual orientation.
"Our sex and relationship education guidance makes it clear that schools should not promote any sexual orientation. The DfE will be looking into these schools."