The gulf between the numbers of rich and poor children winning university places has reached record levels, figures from Ucas show.
Students who received free school meals - the long-time indicator of poverty - are less than half as likely to enter higher education than those who do not get the dinners, the biggest gap in recent years.
While there has been a steady increase in the entry levels among less wealthy students over the last 10 years, an increase of 78% proportionally, this has slowed sharply since 2015, according to the organisation's annual report.
The figures will come as a blow to Prime Minister Theresa May, who put slashing inequality at the heart of her Government's ambitions when she took office in July.
The analysis of entrants for the majority of UK universities in the last year also showed:
:: A pre-Brexit spike in students from the EU taking places at UK institutions, while overseas students entering higher education in this country dropped for the first time since 2011.
:: A persisting gender gap between those accepting university places - with women now a record 35% more likely to take places than men.
:: The highest-ever number of 18-year-olds accepted to university this year.
:: White people still ranking as the lowest ethnic group for entry rates.
The UK university acceptance rate for more advantaged students is increasing around five times faster (up 1.4 percentage points to 32.8%) than for their poorer peers who are on free dinners (up 0.3 percentage points to 16.1%).
While this marks an all-time high for the amount entering university from both demographics, the difference in growth widens the gap between rich and poor to its largest since 2006.
This 16.7 percentage point difference is the "largest recorded value" between the two groups, Ucas said.
Free-school meal students make up between 12 to 15% of state school students aged 15, Ucas said - but they compose almost 60% of the most disadvantaged group of children applying to university.
This fifth of the English population who are least likely to go to university - chiefly composed of poorer, state-educated pupils from areas where fewer people attend university - have only seen a marginal increase in applications (up 0.1 percentage point this year to 13.6%). The cross-section is also largely made up of people who are white and male.
This bucks a recent trend which saw the difference between the most advantaged top fifth and least advantaged bottom fifth of youngsters narrowing in terms of entry. A jump in the most-advantaged accepting places has led to this to grow again.
An extra 40,000 students from the bottom group would be needed to close the difference, Ucas said.
Chief executive of Ucas Mary Curnock Cook said: "When she entered Downing Street in July, the Prime Minister pointed out that white working-class boys are the least likely to go to university.
"Our report underlines this point, showing that nearly three quarters of the group least likely to enter university are men, most are from lower income families, and nine out of 10 are in the White ethnic group.
"Although the number of students from disadvantaged backgrounds entering higher education has reached record levels again this year, there are early signals that the good progress made in recent years may be slowing down.
"The best way to get on track to better progress is to focus efforts on improving GCSE outcomes for all children which we know is the primary driver of increased entry rates to higher education."
Universities and Science Minister Jo Johnson said: "It is welcome news that record numbers of students secured places at university this year and that people from disadvantaged backgrounds are now more than a third more likely to enter higher education than in 2010.
"However, we know there is more to be done if we are to truly make this a country that works for everyone.
"That is why this Government has put social mobility at the top of its agenda. Our reforms are raising standards - there are now 1.8 million more children in good or outstanding schools than in 2010 and through our Higher Education and Research Bill, we are ensuring all institutions go further and faster to promote social mobility."
Alan Milburn, chairman of the Government's Social Mobility Commission, said: "It is clear from these figures that the current approach on widening access to our universities had reached its limits.?
"Universities must raise their game to ensure that education is genuinely accessible for all, regardless of background.
"It is time the Government published social mobility league tables annually to highlight which universities are doing most and which least to widen access, improve retention and ensure good careers for their students.
"Poor performers in widening participation should be challenged to raise their game. Charging £9,000 fees should be subject to universities reaching a higher bar in access, retention and progression for low-income students than they do currently.
"A set of floor standards could raise this bar, linking higher fees to data on outcomes for young people from low-income and low-participation backgrounds.
"Big changes are needed if universities are to play a bigger role in improving Britain's woeful social mobility story."