All bright children should be given the chance to go to private school, an education expert said today, as he warned that the UK's schools are socially divided.
Academic selection of pupils, widespread in the 1970s, has been replaced by social selection, according to Sir Peter Lampl, chairman of the Sutton Trust.
It is now more difficult for poorer children to improve their chances in life than in the past, he argued.
Speaking at the Headmasters' and Headmistresses' Conference (HMC) annual conference in Belfast today, Sir Peter urged heads to back a scheme aimed at allowing more bright children from all backgrounds to gain places at private schools, based on merit rather than ability to pay.
Social mobility - improving an individual's life chances - is "the biggest social issue of our time", Sir Peter said, and is "on the political map like never before."
A study conducted for the Sutton Trust by the London School of Economics (LSE) found that Britain, together with the United States, have the lowest levels of mobility of any developed country for which there is data, he told the conference.
"Put simply, it is very difficult for children from less privileged backgrounds to move up in society and it is more difficult than it used to be. It's got worse."
Sir Peter also cited an international study which found that inequality has increased faster in Britain over the last 30 years than any other developed country, and is one of the highest in the world.
"We got rid of academic selection in the 1970s and this has simply been replaced by social selection," Sir Peter said.
He added: "Our selective universities and many of our professions are effectively closed to a large number of young people."
Some 7% of English pupils go to private school, and another 4% attend selective grammar schools. These grammar schools attract just 2% of youngsters on free school meals - a measure of poverty.
And the top comprehensive schools take just 6% of their pupils from the poorest homes, Sir Peter said.
"I believe we should address this inequality in three ways.
"First comprehensives should use ballots to determine admissions to urban secondary schools to ensure a social mix."
Secondly, grammar schools should reach out to able students from poorer families.
"The third solution should be to transform the independent sector, ensuring that day schools recruit once again on merit rather than money, opening them up to a wider pool of talent."
Initiatives such as private schools sponsoring academies and free schools are "worthy but small scale", Sir Peter said.
"They won't do more than drill a small hole in the barrier between sectors."
Sir Peter called on heads at the conference to sign up to the Open Access scheme, which aims to make private day school places available to more than 30,000 able children whose parents could not afford full fees.
More than 80 independent day schools have already backed the initiative, he said.
The scheme was trialled at the Belvedere School in Liverpool over a seven year period, and saw results improve and a wider social mix of pupils.
Three in ten girls from low income backgrounds were given free places and a further four in ten more received help with fees. The others paid full fees.
Sir Peter told heads: "Open Access membership would be voluntary, but only schools of sufficient academic quality would be admitted."The only pressure would come from schools' desire to educate able children from all backgrounds, and their need to compete with a new dynamic sector drawing on a wider talent pool."