A staggering 59% of the Cabinet went to the universities of Oxford or Cambridge, compared to the average of less than 1% of the public as a whole, according to the research from The Social Mobility and Child Poverty Commission, which said it was concerned about stagnant social mobility in the UK.
Top cabinet members including David Cameron, George Osborne, Nick Clegg, William Hague and Theresa May all attended one of the two universities.
Around 36% of the Cabinet also went to private schools, compared to only 7% of the public as a whole.
A third of all MPs (33%) and 22% of the Shadow Cabinet went to private schools, the report found.
The findings for politicians mirrored the wider trend for other influential positions in society.
Those who have studied at Oxford or Cambridge make up 75% of senior judges, 50% of diplomats, 44% of public body chairs.
The figures are drastically disproportionate with the national average of less than 1%.
More than one in three (38%) of members of the House of Lords also went to Oxbridge.
People who have studied at private schools also dominate the top jobs. They make up 71% of senior judges, 62% of senior armed forces officers, 53% of senior diplomats, 50% of members of the House of Lords and 44% of the Sunday Times Rich List.
Judges are the professional group with the most advantaged educational backgrounds, according to the report.
One in seven judges (14%) went to one of just five private schools: Eton, Westminster, Radley, Charterhouse and St Paul’s Boys school.
Areas of the media industry were also revealed to be dominated by the two Oxbridge universities: 47% of newspaper columnists and 33% of BBC executives studied at Oxbridge.
The Social Mobility and Child Poverty Commission, which is a non-departmental government advisory body, said it was deeply concerned about the dramatically elitist society which it said its report had uncovered.
While it acknowledged that many of the most intelligent individuals attend top schools and universities, the commission said that the disproportionate number of privately and Oxbridge-educated people in top jobs suggested a chronic lack of social mobility in the UK, and that those reaching the highest positions were not always doing so through merit.
Alan Milburn, the chair of the commission, said: "The risk... is that the more a few dominate our country’s leading institutions, the less likely it is that the many believe they can make a valuable contribution.
"A closed shop at the top can all too easily give rise to a ‘not for the likes of me’ syndrome in the rest of society."
He added: "We in the Commission hope this report prompts a re-think in the institutions that have such a critical role to play in making Britain a country where success relies on aptitude and ability more than background or birth."
Top sporting figures are also likely to have studied at private schools: 35% of national rugby teams and 33% of the England cricket team were found to have attended private institutions.
By contrast, local government is far more representative of the population than other professions covered in the research.
A more moderate 15% of local government leaders and 8% of local government CEOs have studied at private schools. This compares with 55% of Whitehall Permanent Secretaries.