Simon Calvert of the Christian Institute says forcing teachers to promote gay relationships would be making them choose between their faith and their job

Schools should be forced to promote gay relationships in sex education lessons, union leaders say.

The National Union of Teachers has called for a ‘positive portrayal of same sex relationships’ in lessons to be made ‘compulsory’ under the next government.

It said MPs had a duty to tackle ‘homophobia, biphobia and transphobia’ in schools and create a ‘positive climate of understanding about sexuality’.

But critics accused the NUT of ‘thought control’ and said the ‘intolerant’ proposals risked ‘oversexualising’ children at a young age.

Meanwhile, Christian groups warned it would compel teachers at faith schools to act against their beliefs.

However, the union said the changes were needed to tackle prejudice which was ‘still strongly prevalent in our schools’.

Simon Calvert of the Christian Institute said: ‘This motion is itself an act of intolerance towards mainstream Christians and their beliefs. It would force Christian teachers to have to choose between their faith and their job.

‘I wonder whether Christian members of the NUT who have paid their dues can expect any help from the NUT when their jobs are on the line.’

He added that Church schools already teach ‘love and tolerance’ of others without having to explicitly approve of same sex relationships.

The proposal was contained in a motion on lesbian, gay, bisexual and transgender (LGBT) rights passed by the NUT at its annual conference in Harrogate yesterday.

It stated: ‘Conference instructs the executive to call upon the present and future government to … make it compulsory that all schools’ sex education policies include a positive portrayal of same sex relationships.’

The NUT said only 10 per cent of LGBT teachers felt confident to be ‘out’ to students.

Other proposals included promoting LGBT History Month – which celebrates gay and transgender rights movements – in every school.

The motion also advocated supporting transgender students and staff ‘while transitioning and after’.

Christine Blower, NUT General Secretary, said: ‘We need education policy that develops curriculum for children and young people that supports the democratic values of a diverse Britain – including LGBT equality.’

Christine Blower, National Union of Teachers General Secretary, has called for a ‘positive portrayal of same sex relationships’ in lessons to be made ‘compulsory’ under the next government

The law would also see teachers at Muslim and Jewish schools compelled to promote gay marriage and other issues that go against their beliefs.

The proposal comes amid a row over the government’s new requirement for schools to teach ‘fundamental British values’, which include tolerance of other faiths and lifestyles.

Christian schools have complained they were branded ‘intolerant’ and marked down by Ofsted after children were asked about gays and lesbians.

Durham Free School is set to close after inspectors branded it an educational failure and said some children displayed ‘discriminatory’ views towards people of other faiths.

Meanwhile, Grindon Hall Christian School in Sunderland was put in special measures after failing to meet Ofsted’s British values criteria. Inspectors were said to have asked pupils if they knew what lesbians ‘did’ and if any of their friends felt trapped in the ‘wrong body’.

The drive was formed in response to the Trojan Horse scandal in which Muslim hardliners allegedly tried to impose an Islamic agenda on schools in Birmingham.

The NUT motion renewed fears teachers would be required to go beyond their remit in tackling such a sensitive subject.

Andrea Williams from Christian Concern said: ‘This kind of policy is dangerous for our children who are being oversexualised at a very young age.

Durham Free has been told to close after inspectors branded it an educational failure and said some children displayed ‘discriminatory views’ toward people of other faiths

‘They are being introduced to concepts and having normalised same sex relationships which robs them of their innocence and is not good for their emotional and moral wellbeing.’

Chris McGovern, of the Campaign for Real Education, said: ‘The rights of groups who oppose gay marriage on sincere religious grounds should be respected as much as those who support gay marriage. Thought control should not be promoted by the NUT.’

A Church of England spokesman said it is ‘fully committed to sex and relationship education that allows room for exploration and discussion of relationships, within a framework of Christian values’.