More than half of the leading figures in UK politics, law, medicine, business and journalism went to independent schools, research suggests.
Most judges went to university in Oxford or Cambridge
A survey of 1,000 people for the Sutton Trust said the proportion had fallen only marginally in the past 20 years - from 58% a generation ago, to 53%.
However, among those who had been to a UK university the proportion from Oxbridge fell from 61% to 47%.
New prime minister Gordon Brown is a graduate of Edinburgh University.
PRIVATELY EDUCATED 2007
Lee Elliot Major of the Sutton Trust, an educational charity, compared the school and university background of 500 people currently at the top of their fields with 500 similarly successful people 20 years ago.
He found 53% of today's leading figures across five different sectors had been educated at independent schools. Overall, private schools educate just 7% of school-age children.
A generation ago, 58% of leading people in the same sectors had been privately educated.
Just under a third of the leading figures today were educated at grammar schools, while only 17% went to state comprehensives.
Dr Elliot Major said: "This analysis shows that the school you attend at age 11 has a huge impact on your life chances, and particularly how likely you are to reach the top of your chosen profession.
"We are still to a large extent a society divided by wealth, with future elites groomed at particular schools and universities, while the educational opportunities available to those from non-privileged backgrounds make it much more difficult for them to reach the top."
The highest concentration of Oxbridge graduates was found to be among judges: 78% of those surveyed in 2007 had been to university at Oxford or Cambridge, compared with 87% in 1989.
Judges were also the most likely to have been privately educated, the research suggests. In 2007, 70% were from independent schools while in 1989 the figure was 74%.
This year 42% of the politicians surveyed were ex-Oxbridge, compared with 62% in 1974.
The chairman and founder of the trust, Sir Peter Lampl, said: "The first priority should be to improve our underperforming state schools but we also need to recognise that we have a socially selective school system.
"The top 20% of our secondary schools - independents, grammars and leading comprehensives - are effectively closed to those from non-privileged backgrounds.
"We should open up independent day schools to children from all backgrounds on the basis of merit alone."
According to the study, politicians were the least likely to have been privately educated, with 38% from independent schools in 2007 and 46% in 1974 (the last time a Labour government was in power).
The group also had the largest proportion of leading members from state comprehensives: over a third in 2007.
The biggest decline in independently-educated people had been among the business community.
The Sutton Trust looked at chief executives of FTSE 100 companies. In 1987, 70% of those educated in Britain had been to private schools. In 2007 it was 54%.
But the charity said more of them - just over a third in all - were now non-British and had been educated abroad, compared with less than a tenth a generation ago.