The Archbishop of Wales has warned that allowing 16-year-olds to opt out of prayer in assembly could lead to the marginalisation of religion in schools.

Writing in the Times Educational Supplement, Dr Barry Morgan said letting sixth-formers withdraw from collective worship could leave them “narrowly focused on personal attainment”.

"Collective worship has been branded as something that young people grow out of by the age of 16, at precisely the time when it might be the best way of feeding both their minds and their hearts as they start to explore the responsibilities and consequences of adult life," he said.

"I am concerned that this is the thin end of the wedge and could be just the start of a process that devalues and ultimately marginalises the provision of collective worship in schools.”

All schools are required by law to offer a daily act of worship along Christian lines but two years ago England gave the right to sixth form pupils to opt out of participating. A law was introduced in Wales earlier this year giving 16-year-olds there the same entitlement.

The British Humanist Association was among those defending the opt-out. The BHA said it did not think that there should be compulsory collective worship, but while it was still taking place in schools “children should be allowed to opt out if they want”.

The Archbishop warned of schools turning into a “bland secular wasteland”. He said that a shared spiritual experience was a “chance for pupils to participate fully in, reflect on and respond to life and religious issues”.