Teenagers from poorer backgrounds remain much less likely to go to university, and to study at a top institution, according to a report by the Higher Education Funding Council for England (HEFCE).
It also issued a warning that some universities could run into trouble if they fail to attract enough students and raised concerns about a major slump in the numbers of people studying part time.
The new study looks at the impact sweeping changes to higher education funding have had on universities.
Tuition fees were trebled last autumn, with new undergraduates now charged up to £9,000 a year for a degree course.
Graduates begin paying the loan back once they are earning at least £21,000.
The study says that while the evidence shows that the reforms have not made poorer youngsters less likely to study full time, there are still "significant gaps" between different groups of students.
Official data, published by UCAS, shows that 18-year-olds from the wealthiest areas are still three times more likely to apply to university than those from the poorest areas, the report says.
And entry rates to universities that require top A-level grades are six to nine times greater for students from advantaged areas.
The study says the impact of the reforms on encouraging more disadvantaged young people to go to university are not yet known, and the issue needs to be monitored.
The report also reveals how different institutions have fared in recruiting students since fees were trebled.
It says there is a "mixed picture" with specialist universities and further education colleges the only groups to maintain similar numbers of students between 2010-11 and 2012-13.
It adds that only 13% of universities with the highest entry requirements increased their full-time student numbers, compared to a third of those with the lowest requirements.
"Some institutions with the lowest entry tariffs saw as much as a 15% increase," HEFCE said.
But around half of institutions with lower entry requirements saw their numbers fall by 10% or more, it adds.
The study concludes that England's university sector is in "reasonable financial health", with no institutions facing insolvency in the short term.
But it warns: "There is wide variation in the financial performance and the health of different institutions within the sector, and some institutions will face difficulties if they experience repeated falls in student recruitment."
Overall, figures suggest that the numbers of young people planning on going to university may be recovering after a "dip" last year - the first year of the fee hike, HEFCE's report says.
But it raises serious concerns about part-time students, saying that the numbers of people starting part-time undergraduate courses has fallen by 40% since 2010-11.
This is equivalent to 105,000 fewer students, the report argues.
It says there is emerging evidence that part-time fees rose in 2012.
"Students who might have found the money to pay the previous lower levels of fees may simply be unwilling to pay higher fees, despite the fact that loans are offered on the same terms as for full-time students," the report says.
HEFCE chief executive Sir Alan Langlands, said: "It is difficult to draw firm conclusions at this early stage of the reforms.
"The sector is currently in reasonable financial health, and student demand appears to be recovering after last year's fall.
"But today's report also highlights some causes for concern: in particular, sharp drops in recruitment to part-time courses and a related decline in mature entrants. And although recent positive trends in widening participation appear to have been sustained in the first year of the reforms, disparities in the recruitment and retention of students by social background and gender remain unacceptably stark.
"HEFCE will continue to monitor these and other issues, taking action as necessary."
Under major reforms, last year universities were allowed to recruit as many students as they liked who gained at least two A grades and a B at A-level.
This is being lowered this year to cover students with ABB at A-level.
Around 20,000 places were also set aside for institutions that kept fees below £7,500 - a scheme known as "core and margin".
HEFCE's report says that overall in 2012-13 recruitment to universities fell below planned numbers by around 9%, equivalent to 28,000 places.
A number of universities said that they had departments that were "cautious" in making offers because they did not want to breach their set student limit.
Vice-chancellors' group Universities UK (UUK) today said it was launching a review into part-time study.
UUK president Professor Eric Thomas, said: "We have been concerned for some time about recruitment to part-time courses. It is particularly striking that enrolments to part-time courses have declined despite the recent extension of loans to part-time students.
"These figures show starkly that there is a serious issue, and we are determined to get to the bottom of it.
"That is why Universities UK is pleased to have been asked by the Minister for Universities to review the evidence on part-time study, and to make urgent practical recommendations on how this provision can be developed."
Rachel Wenstone, Nation Union of Students vice-president for higher education, said: "The Government urgently needs to address the decline in part-time student numbers. They have failed to account for less traditional students and forms of learning in making their changes and this is pushing many away from education.
"Part-time student numbers have been falling since the economic crisis began but the Government have created an unsustainable situation by jacking up fees placing a huge burden on potential students.
"Students from disadvantaged backgrounds and older students are more likely to study part-time than others and a lack of investment in part-time study will have disastrous impacts on diversity within universities."