More than 18,000 children were sent to state faith schools against their parents' preferences in England this year, an exclusive analysis by the National Secular Society has found.

An NSS study of Department for Education admissions data found that 14% of families who missed out on their first choice of a non-faith school were assigned a faith school in September 2017. The figure included 9,927 admissions to secondary schools and 8,126 to primaries.

The data also showed that the supply of faith-based state primary schools (37%) is significantly ahead of demand (29%). Seventy-one per cent of primary parents put non-faith schools as their first choice this year, while the figure was 81% at secondary level.

NSS education and schools officer Alastair Lichten said: "We've long dealt with the problem of families losing out on their choice of local school due to discriminatory admissions. But the other side of that coin is that we are increasingly hearing from families with no choice but a faith school.

"This situation is exacerbated by the increasingly non-religious population, unpopular – and therefore undersubscribed – minority faith schools, school amalgamation biasing against secular schools and a lack of secular provision in rural communities.

"It's unacceptable that so many children are being given a faith-based education when their parents do not even want it for them. The government must take steps to address this."

The findings follow the publication of research in January which showed that faith-based provision is treated preferentially during school reorganisations.

In response Lord Agnew, the minister with responsibility for faith schools, stressed local authorities' responsibility to "ensure there are the right number and types of places to both meet demand and to provide diversity and choice for parents".

Research suggests faith is not an important reason why parents choose schools. In 2013 figures from YouGov showed that only 5% of parents in Britain would choose a school on the basis of giving a "grounding in faith tradition" and only 3% for "transmission of belief about God". In the same survey just 32% of people thought the government should prioritise funding for "faith schools in general".

After the latest revelations Mr Lichten added that "ultimately the taxpayer should not fund faith-based education".

"The future of England's education system should be to educate children of all backgrounds together in inclusive, secular schools, where they are trusted to make their own minds up about religion."

This article was originally posted on the National Secular Society website on 9 April 2018.