Religious schools that select pupils on the basis of faith make up almost 50% of the "worst offenders" when it comes to admitting poor pupils, research has suggested.
Just 16% of all schools in the UK admit their pupils on the basis of their religious background.
But in a list of secondary schools which have the lowest numbers of pupils on free school meals, 46% were faith-based.
When it came to pupils with English as a second language, another indicator of poverty, 50% of the schools with the lowest number were faith schools.
The research by the Fair Admissions Campaign looked at every mainstream secondary school in England, and have compiled a map of each school, its religious character, and the socio-economic indicators about the kind of pupils who attend.
The results, the secularist campaigners say, shows how faith schools have a segregating effect on social and ethnic inclusiveness.
Rabbi Dr Jonathan Romain, chair of the Accord coalition, which opposes faith schools, said the research shows the "hypocrisy" that faith schools serve as a fair reflection of communities. "They not only further segregate children on religious and ethnic grounds, but also are skewed towards serving the affluent at the expense of the deprived.
"The data poses some very awkward questions for the state funded faith school sector, especially as many people of faith are appalled that schools that should focus on the poor have become so elitist."
Professor Ted Cantle, who chaired The Cantle Report into the 2001 race riots, called it the "increasing balkanisation of our school system, with children growing up in separate communities with little chance of learning about others.
"It shows that education has done nothing to break down the “parallel lives” I described in 2001, rather they have been reinforced."
The Church of England’s Chief Education Officer the Revd Jan Ainsworth said the Church, having started the first national system of schools 200 years ago, was "proud of the way in which our schools enable children from disadvantaged backgrounds to succeed".
Ainsworth said the Department of Education’s 2013 School Census, showed that 15% of pupils at CofE Secondary pupils are eligible for Free School Meals, the same as the average for non CofE schools.
"Church schools are a central part of our mission to serve the common good," said Ainsworth. "That is why around the country, they are open to children of Christian faith, of other faiths and of none.
"Over the next few years, one of our priorities will be to ensure that more children can benefit from the excellent education they provide. “
Comprehensive secondaries with no religious character admit 11% more pupils eligible for free school meals than would be expected given their areas, with Church of England secondaries admitting 10% fewer; Roman Catholic secondaries 24% fewer; Jewish secondaries 61% fewer; and Muslim secondaries 25% fewer.
The most segregated local authority as a result of religious selection is Hammersmith and Fulham, the research showed. While 15% of pupils nationally are eligible for free school meals, the segregation between the religiously selective schools and other schools is almost double that, 27%.
Andrew Copson, Chief Executive of the British Humanist Association, commented: "Today’s findings make clear like never before the devastating effects that faith-based admissions have in segregating communities along socio-economic and ethnic lines."
Bishop John Pritchard, head of education for the Church of England, previously suggested in a September 2013 report for religious think-tank Theos, that faith schools were not the cause of segregation, saying the schools were "acting as a battleground on which to fight larger battles about the role of religion in an increasingly plural society."
He told the General Synod that 15% of pupils are eligible for free school meals at Church of England secondary schools, in line with the national average.