Alarm over a 40-per-cent drop in part-time students registering for university courses is being expressed by the Office for Fair Access - the university access watchdog.
In its annual report published today, it reveals that the number fell by 105,000 between 2010/11 and 2012/13.
The fall coincides with a significant slump in the number of mature entrants opting for higher education study (7.1 per cent) - both routes often chosen by students from disadvantaged backgrounds to bolster their chances of employment.
"I am very concerned by the significant decline in part-time and mature numbers as students in these groups are more likely to be from groups under-represented in higher education," said Professor Les Ebdon, OFFA's director.
"If higher education is truly to meet the needs of all those with the talent to benefit, it must be flexible enough to support those who choose to study later in life whether part-time or full-timer as well as those who go straight to university from school."
Professor Ebdon said he believed it was possible that the new funding arrangements for students - under which part-timers can secure loans - had not been promoted sufficiently well.
He also warned universities not to become complacent about a rise in student applications this year compared to the first year of the new system of charging up to £9,000 a year for courses.
"This is because it's likely that students who applied for entry in 2012/13 and 2013/14 had already made up their minds to go to university (before the fee changes)," he added. "In future we will see students applying whose minds were not yet made up when the new system was introduced and we cannot be sure how they will respond."
Rachel Wenstone, vice-president of the National Union of Students in charge of higher education, added: "Part-time and mature students are often forgotten but support for them is vital to widening access to higher education.
"Both groups are likely to have more debt and less likely to receive financial support from their families than other groups and older students are much more likely to consider dropping out of their courses."