The clause was part of the 1988 Local Government Act and although it has never been challenged in the courts, it has created a climate of self-censorship for librarians and artists working in schools, said Jennifer Edwards, the campaign director.
She has written to Chris Smith, Secretary of State for Culture, Media and Sport, pressing him to persuade the deputy Prime Minister John Prescott, to repeal the clause.
Her appeal follows one made by the British Medical Association in a report published last May which said that the clause had proved "positively harmful" to sex education in schools. It had undermined the ability of schools to give neutral advice and support to young people by sowing confusion and concern.
Ms Edwards said she hoped that the Government would remember that it had voted against the clause when it was in opposition: "It is time that this anachronistic and pernicious law was swept from the statute book."
The fact that the clause had never been a cause cel bre in the courts meant that nobody knew just how much self-censorship went on. Anecdotal evidence, however, showed that librarians and theatre-in-education companies had been extra cautious in their choice of books and plays lest "some backwoodsman councillor" accused them of promoting homosexuality, she said.
In fact, the clause does not apply to schools but to local authorities, and sex education is the responsibility of school governors, not the local authority. But the BMA and the Sex Education Forum as well as the NCA have ample evidence that teachers wrongfully used it as an excuse not to teach about homosexuality.