The Government has rejected calls to include the study of humanism in the new Religious Studies GCSE, despite widespread support for its inclusion. Campaigners have been left "bitterly disappointed" at the omission.

Though references to humanism are included, the revised content will not include the study of humanism alongside  major world religions.

At GCSE level, students are required to study two major faiths out of Christianity, Catholicism, Judaism, Islam, Hinduism, Sikhism and Buddhism. While it is hoped that this will increase religious literacy, critics believe that pupils should have the option to undertake in-depth study on a non-religious or humanist worldview.

The British Humanist Association (BHA) carried out a public consultation and found that 90 per cent of the public supported its call. The BHA was asked by the Department of Education to produce the content of an 'annex' on Humanism, but it was not included in the final revised content.

The group has branded this decision "inexplicable".

The BHA has been supported by the Religious Education Council and the National Association of Teachers of RE. More than 100 leading philosophers, academics and consultants signed a letter to Minister of State for School Reform Nick Gibb calling for the annex to be included, and 30 faith leaders, including former Archbishop of Canterbury Rowan Williams, also signed a letter urging the government to reconsider.

"As religious leaders we are writing to express our support for proposals to allow students to have the option for systematic study of Humanism...and for an annex setting out content on Humanism to be added alongside existing GCSE annexes on the principal world religions," the letter read.

"Such a change would not compel anyone to systematically study non-religious worldviews or make it possible to do so for the whole of a qualification, but it would allow young people to study a more representative sample of major worldviews that are common in Britain today."

Signed by representatives including the Rt Rev Richard Harries, former Bishop of Oxford, Rabbi Dan Cohn-Sherbok, a Professor of Judaism, and Raheed Salam of the Interfaith Youth Trust, the letter added that including humanism "would be fair, popular, and add rigour to the subject".

"We see no reasonable or persuasive argument to oppose it," it concluded.

However, GCSE pupils will not study comprehensive content regarding a non-religious worldview. According to ministers, it would be inappropriate to do so.

"As these are qualifications in religious studies, it is right that the content primarily focuses on developing students' understanding of different religious beliefs," the government has said.

"A simultaneous focus on humanism would detract from an in-depth treatment of religion and the comparative study of two religions."

The content will include, however, some new inclusive references. Students will be required to develop their "knowledge and understanding of...non-religious beliefs, such as atheism and humanism', and to "demonstrate knowledge and understanding of the fact that...religious traditions in Great Britain are diverse and include...non-religious beliefs, such as atheism and humanism."

BHA Chief Executive Andrew Copson has welcomed these additions, but says the group is "bitterly disappointed that Humanism is to be largely excluded".

"With each generation being less religious than the previous one, it is vital that humanism be included and there is barely anyone apart from the Conservative part of the Coalition Government that disagrees. Today's political decision is unfathomable and time will prove its futility," he said, adding that school pupils have been "let down" by ministers.