Students who slack at university will earn around £80,000 less in their lifetime than their counterparts who work harder, an official Government study has concluded.
Economists, working on behalf of the Department of Business, estimate that men who get a 2:2 degree will earn just £65,000 more in their working life than if they had left school after 'A' levels.
In contrast men who get either a First or a 2:1 will be £141,000 richer than if they had gone straight into the workforce.
Women fair marginally better - with an average female graduate earning an additional £100,000 for a 2:2 over her non-university educated counterpart - but the premium for a better degree is still £85,000.
Given most students now face repayable university tuition fees of £27,000 and can claim living costs loans of around £21,000 over three years, the study raises serious questions about the financial sense for some students going to university in the first place - if they are not prepared to put the hours.
A student in London claiming the maximum in loans and fees and getting a 2:2 at the end of their three years at university would, over their lifetime, be only £15,000 better off than if they had not gone to university at all.
The findings are contained in an official Government research paper released to coincide with 'A' level results. Carried out by academics at the universities of Lancaster and Kent it found that going to university in general still made financial sense despite the high cost.
They estimated that the return to a degree relative to two or more A-levels but no degree was 23 per cent for men and 31 per cent for women.
But within that there were marked discrepancies. Students studying medicine at university will be over £400,000 richer than if they had got another job after school compared to students studying mass communications who will only earn £3,000 extra.
Women who study economics will make nearly £1 million more over their lifetimes while for men the figure is only £300,000.
Women with degrees are more likely to follow similar career structures to men - something not seen in women who leave school without a higher education qualification.
Interestingly the study found no evidence that the expansion of higher education in the late 1980s and early 1990s had had any appreciable effect on differential earnings.
One of the authors of the study, Professor Ian Walker from Lancaster University, said the reason for this might be because of the increasing premium put on skills - particularly the "computerisation of the workforce".
"There have been huge technological changes in the workplace over the last 30 years or so which has favoured the skilled worker," he said.
"What we are seeing is increasing financial returns for skill."
Professor Walker speculated that the difference in earnings between those students who got 2:2s and those who got higher class degrees might be down to a general willingness to put in effort.
"Every year we take on around 800 first year economics undergraduates," he said.
"They have all got 'A's and 'B's in their exams and are smart kids. Yet I know from past experience that 40 per cent of them are not going to do well in their degrees. What I can't say is which ones they will be.
"Some think that they can learn economics in two weeks at the end of the year. I'm not saying economics is hard but that rarely works.
"It is possible that it is an attitude that they repeat in the work place."
Universities and Science Minister David Willetts said the report showed that university was still worthwhile despite the increases in cost.
"As students discover their A-Level results this new data highlights just what a great long-term investment university is," he said.
"A degree remains one of the best pathways to achieving a good job and a rewarding career - as well as a hugely enjoyable experience for most students."