Just a day after vice-chancellors said they wanted tuition fees to more than double to over £6,000, new research shows some students will earn little more than those getting a job straight from school or college.
Students on arts and humanities courses - along with those failing to get at least an upper-second class degree - are most likely to miss out on the highest-paid jobs, said the Warwick University study.
It comes despite Government claims that a degree "comfortably" adds more than £100,000 to students' lifetime earnings.
The claims have been used to justify higher tuition fees, with students expected to share the burden of paying for university.
Yesterday, it was revealed that vice-chancellors wanted the existing £3,100 fee to rise to around £6,500 to maintain decent teaching standards at institutions in England.
The conclusions were made despite claims that a similar increase would result in students accumulating debts of more than £32,000.
In the latest study, the Warwick academics warned that "any substantial increase" in fees risked preventing teenagers from going to university, particularly those from poor backgrounds.
It came as a hundreds of students from across England prepared to lobby MPs on Wednesday as part of a campaign to prevent further fee rises.
The protest - organised by the National Union of Students - is being backed by David Blunkett, former Education Secretary.
Speaking before the event at the House of Commons, Mr Blunkett said: "Whilst it is clear that no government is going to pull the financial plug on the university sector by simply abolishing fees, it would at this time of global financial downturn, be unacceptable to lift the cap and have a free-for-all across universities."
In the latest study, academics tracked almost 3,000 men and women born in the same week in April 1970.
Professor Robin Naylor and Dr Jeremy Smith assessed how much the average person earned age 30 in 2000 - broken down by their qualifications.
Overall, men who completed undergraduate degrees earned an average of £12.65 an hour, compared to £10.57 for people who got jobs after A-levels. Among women, degree graduates earned £10.81 and those who simply did A-levels were paid £8.23.
The study showed that students with a "good" degree - a first or 2:1 - earned more than those who left with a 2:2 or third-class honours.
Graduates with degrees in social sciences - including economics, law and politics - also earned the most, with men being paid an average of £14.38 and women £12.78. But those taking arts and humanities courses had relatively lower wages, with men earning £12.99 and women £10.56.
The latest study said investing in degree courses was still "an attractive proposition", but the huge variation between students' average earnings meant many could expect "potentially much lower" wages.
"This implies that any substantial increase in the regulated maximum for top-up fees risks deterring participation in higher education, at least for potential applicants from less financially privileged backgrounds," said the researchers. (By Graeme Paton, Education Editor Last Updated: 2:40PM GMT 17 Mar 2009)