Hundreds of schools are to defy government recommendations by refusing to teach non-religious views in RE lessons.
Charles Clarke, the Education Secretary, said philosophies such as humanism should be taught as part of a new "inclusive" approach to the subject.
The Government's long-awaited national framework for RE, launched last week, said children as young as five should be allowed to question the existence of God.
But this week advisers to the country's biggest inner-city education authority, Birmingham, said humanism had no place in the classroom. The city makes no mention of secular ideas in guidelines sent out to its 450 schools in 1995, the last time its syllabus was revised. Guy Hordern, a former Conservative councillor and chairman of Birmingham's Standing Advisory Council for RE (Sacre), said he doubted if the new framework would alter its stance.
"A non-religious view of the world is not appropriate in religious education lessons," he said. "You want to use the limited time available in RE to teach about religion. Secularism is not a religion. Maybe there are people who do not believe in God but, in the main, that's because they have never had a case for the belief of God presented to them."
Birmingham's RE advisers will meet in coming weeks to discuss the framework, but it is believed they will refuse to bow to pressure to introduce humanism.
The framework, which was years in the writing, and is supported by representatives of all faiths, is intended to raise the profile of the subject following worries that it has become increasingly marginalised. At the moment, RE is compulsory for pupils but it is left to the 151 local authorities in England to draw up their own syllabuses.
Critics say this fragmented system has led to wildly differing standards and contributed to a massive teacher shortage.
The national framework was welcomed by religious groups last week but the views of Birmingham's advisers are likely to lead to calls for the guidelines to be made compulsory.
Dr Kenneth Stevenson, the Bishop of Portsmouth and chairman of the Church of England's education board, is the most high-profile figure to call for the framework to be statutory. His view is supported by most teachers.
But Marian Agombar, chairman of the National Association of Sacres, said:
"Very few Sacres have a problem with some teaching of secularism where appropriate. " Other critics of the framework say it does not contain enough secular views.
The Institute for Public Policy Research think-tank has recommended that the title "religious education" should be replaced by "religious, philosophical and moral education", as in Scotland.
Keith Porteous Wood, executive director of the National Secular Society, said: "The framework makes a passing reference to creating 'opportunities'
to study 'secular philosophies such as humanism'. These are overwhelmed by the huge emphasis on the desirability of a religious, particularly the mandatory Christian, lifestance."