The UK is "deeply elitist" according to new analysis of the backgrounds of more than 4,000 business, political, media and public sector leaders.
Most senior judges in England and Wales went to private schools and Oxbridge
Small elites, educated at independent schools and Oxbridge, still dominate top roles, suggests the Social Mobility and Child Poverty Commission study.
It says key institutions do not represent the public they serve.
Commission chairman Alan Milburn said they had to open their doors to a broader range of talent.
"Locking out a diversity of talents and experiences makes Britain's leading institutions less informed, less representative and ultimately less credible than they should be," warned Mr Milburn in his foreword to the report.
"This risks narrowing the conduct of public life to a small few who are very familiar with each other but far less familiar with the day-to-day challenges facing ordinary people in the country.
"That is not a recipe for a healthy democratic society."
The commission says its findings are based on one of the most detailed analyses of its type ever undertaken.
It found that those who had attended fee-paying schools included:
- 71% of senior judges
- 62% of senior armed forces officers
- 55% of permanent secretaries (the most senior civil servants)
- 53% of senior diplomats.
Also privately educated were 45% of chairmen and women of public bodies, 44% of the Sunday Times Rich List, 43% of newspaper columnists and 26% of BBC executives.
In sport, 35% of the England, Scotland and Wales rugby teams and 33% of the England cricket team also went to private schools.
David Cameron meeting officer cadets at Sandhurst - some 62% of senior armed forces staff were privately educated
In politics, half the House of Lords attended independent schools, along with 36% of the cabinet, 33% of MPs and 22% of the shadow cabinet.
This compares with 7% of the UK population as a whole.
Figures for top people who went to Oxford and Cambridge paint a similar picture.
Some 75% of senior judges, 59% of the Cabinet, 57% of permanent secretaries, 50% of diplomats, 47% of newspaper columnists, 38% of the House of Lords, 33% of the shadow cabinet and 24% of MPs hold Oxbridge degrees.
In contrast, less than 1% of the whole population are Oxbridge graduates while 62% did not attend university, says the study.
The report describes the figures as "elitism so stark that it could be called social engineering".
The authors recognise that many talented people attend independent schools and top universities, with 32% of those with AAA or better in last year's A-level results attending private schools.
However, they ask whether top jobs are about what you know or who you know and whether some talent is being locked out.
The report calls for a national effort to "break open" Britain's elite, with:
- employers publishing data on the social background of staff
- university-blind job applications and non-graduate entry routes
- the government tackling unpaid internships that disadvantage those too poor to work for nothing
- senior public sector jobs being opened up to a wider range of people.
The Sutton Trust, which campaigns for greater social mobility through education, welcomed the recommendations.
"It is clear more needs to be done at government level to address the issue," said policy director Lee Elliot Major.
Prof Steve West, chairman of the University Alliance group of business and technology-focused universities, urged a "major rethink of what success looks like in the 21st Century".
"There is a massive breadth of routes to success and huge diversity of opportunity in the global, technology-rich graduate employment market."
A spokeswoman for Oxford University said the institution devoted "a huge amount of resource to widening access and student support" but added that diversifying intake would require wider action.
"Social mobility is an issue stretching back to birth and beyond and early inequality of attainment is one of the major barriers to progression."
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