Faith schools – particularly those which perform well academically – under-represent the rates of social disadvantage in their catchment areas in all three nations of Great Britain, a study has found.

A report from the Sutton Trust, Selective Comprehensives Great Britain, studied the gap between the rates of children receiving free school meals (FSM) in local areas and among schools' intakes.

It found that faith schools are "among the most socially selective of schools both in England and Wales" and are more socially selective than their non-denominational counterparts in Scotland.

Highly-rated faith schools admitted just 11.4% of FSM pupils in Wales, 10% less than the proportion of FSM pupils in the local catchment areas (21.1%). Across all faith schools in Wales there was a 5.5% FSM gap.

In England the gap at highly-rated voluntary aided (VA) schools – which are usually run by religious groups and allowed to discriminate in all their admissions – was six per cent. This was three times higher than in highly-rated non-faith schools. The gap in all VA schools was four per cent.

The report also found that FSM gaps are over twice as large in schools which control their own admissions, compared to those with local authority controlled admissions.

This week the government announced plans for 14 new VA schools in England. The No More Faith Schools campaign is working to oppose these plans.

The report found smaller FSM gaps at voluntary controlled (VC) schools in England. VC schools tend to be faith schools where religious selection is not generally permitted.

The report also found that complex admissions rules were part of the reason for the gaps in England and Wales.

Sir Peter Lampl, founder of the Sutton Trust, told The Independent: "Faith schools are often socially selective because they have complex admissions criteria and appeals processes that middle-class parents are more able to navigate."

In Scotland the gaps were just under two per cent. Non-denominational schools in Scotland were less socially selective than faith schools (also known as denominational schools): they took slightly more FSM pupils than the proportion in their catchment area.

Almost all of Scotland's state-funded faith schools (also known as denominational schools) are Catholic schools. Defenders of Scotland's Catholic schools often highlight the fact they were originally set up to serve relatively disadvantaged families.

The report suggested "transport issues", "willingness to travel" and "the demographics of their local faith community" may be contributory factors to faith schools' FSM gap in Scotland.

Local authorities control all state school admissions in Scotland.

No More Faith Schools campaigner Alastair Lichten said the report was "a reminder that the idea a faith ethos leads to better academic performance is a myth".

"The Sutton Trust has again shown that much of what passes for better performance from faith schools is the result of social selection. It has also shown that organising schools around a religious ethos excludes children from schools which all taxpayers are funding on the basis of their parents' wealth.

"In England, Wales and Scotland, giving religious groups control of education exacerbates inequality and social division. Meanwhile the more schools are organised along secular lines, the more they help to bring children together."

The Sutton Trust report said the admissions process for faith schools should be "opened up so that their admissions are fairer, and reflect their local population, while maintaining their ethos".

In response Mr Lichten said: "Steps to limit faith schools' ability to discriminate in admissions would be welcome. But ultimately ministers across Britain should be prepared to go further than the Sutton Trust suggests and roll back religious groups' control of schools altogether."