Secretary of State for Education Michael Gove has ordered an investigation into the CES to question whether or not they have broken impartiality rules. The Welsh government has said it will investigate similar complaints about the CES.
It is illegal for schools and teachers in the UK to take a side in a political argument.
It was revealed the CES had invited nearly 400 state-funded Roman Catholic schools to back a petition against gay marriage.
The CES have denied they have broken any rules, saying their feelings on gay marriage are religious and not political. They have said they will continue to appeal to students over the age of 16.
The BHA are currently seeking a pupil who will assist them with legal action.
BHA Faith Schools Campaigner Richy Thompson said: ‘Any gay, lesbian, bisexual or transgender pupil at a school whose head declares that gay marriage and civil partnerships are unnatural is obviously going to feel discriminated against and trapped. Action to remedy this situation cannot come soon enough.’
The BHA believes the CES has broken section 406-7 of the Education Act, which regards political indoctrination and requirement for balance, and section 149 of the Equality Act, which says the public sector such as schools and hospitals has a duty to remain unbiased.
The Pink Triangle Trust (PTT), a UK-based gay humanist charity, has supported the BHA and also condemned the recent suggestion by the Pope’s representative in Britain that Christians, Muslims and Jews should create a united front against gay marriage.
PTT secretary George Broadhead said: ‘This move by the Papal Nuncio should come as no surprise. After all, Islamic groups and Orthodox Judaism are as hostile to LGBT rights as the Roman Catholic Church.
‘It is no less surprising to learn the Archbishop of Southwark is defending the action of Catholic schools. It is outrageous that children attending a state school paid for by taxpayers are being encouraged to be homophobic. Let’s hope the BHA carries out its threat.’
Conor Marron, speaking for pro-gay campaign Coalition for Equal Marriage, said: 'Children as young as 11 should not have to be drawn into political arguments such as this, in fact no school pupil should.
'We must protect freedom of religion and freedom of speech, but at all times any duty of care must come first, most especially when it comes to children.'