The International Certificate of Christian Education (ICCE) has been rubber-stamped by a government agency, even though it is based on a curriculum that says the Bible is the "final authority" on scientific matters. It has prompted outrage from secular campaigners, while schools following the curriculum have come to its defence, saying that it is "academically very sound".

The exams, which are used in at least 34 English private schools and by home educators, are based around the Accelerated Christian Education programme, which originated in Texas, US, in the 1970s. Pupils study a range of subjects including science and English, but spend half their time learning from Bible-influenced US textbooks.

The National Academic Recognition Information Centre (Naric), which rules on the comparability of qualifications in the UK, has approved the exams following an investigation, deciding that they are comparable to mainstream qualifications.

It is the second time that Naric has backed the exams, which it first approved in 2009. Criticism of that decision - and of claims made in history and science textbooks used in the curriculum - drove the agency to review its findings, looking specifically at the exam content.

However, following a second review, Naric - which is funded by the Department for Business, Innovation and Skills - is standing by its decision. "The study highlighted many strengths within the ICCE programme, while also presenting areas for improvement," it said in a statement.

Richy Thompson, schools campaigner at the British Humanist Association, said Naric was failing to ensure that children received a "rigorous" education. "How can a science qualification that is so far removed from the evidence on matters of evolution possibly be worth the equivalent of a Cambridge International Examinations A level in biology?" he said.

However, Paul Medlock, head of the private Maranatha Christian School in Swindon, Wiltshire - where the Accelerated Christian Education curriculum forms a "major" part of children's learning - said that the courses were "academically rigorous".

He said his pupils took ICCE exams in place of GCSEs and A levels and had been accepted by good universities in the UK. Claims made in some of the textbooks, such as that the Loch Ness monster disproves Darwinism, were "interesting discussion points" for pupils, he added.

"We buy into the curriculum and we use it as we see fit; we are not signing up to an ideology," Mr Medlock said. "There are things I wouldn't necessarily align myself with, but these become interesting discussion points for the pupils. Whatever programme you look at, there will be something in it that is inaccurate, as our understanding is changing all the time."