One in four UK graduates reports being overqualified for their jobs, with the OECD saying this may partly be down to some of them lacking basic numeracy and literacy skills.
A 2012 Survey of Adult Skills showed that university-educated adults in England or Northern Ireland were more likely to work in jobs that require lower qualifications, than on average across OECD (Organisation for Economic Co-operation and Development's) countries.
Some 28% of university degree holders in England, and 24% in Northern Ireland, reported being overqualified for their jobs - compared to 14% on average across OECD countries and economies that participated in the survey.
But Andreas Schleicher, OECD's director of education and skills, said: "Some people with degrees don't have the right skills - numeracy and literacy.
"There are people who are not working in graduate jobs and when you test their skills, they don't come up so well.
"You would label them as overqualified, but they may not be overskilled."
He said that one possible reason for this could be the degree having failed to teach graduates maths and literacy to the level they would need for a graduate job.
Speaking at the launch of the OECD's Education at a Glance report, Mr Schleicher said in some cases it was surprising that students had managed to make it onto a degree course in the first place.
He added: "You look at the numeracy skills involved, they are pretty basic. I am not talking about somebody doing advanced mathematical analysis or reasoning, these are pretty basic numeracy skills.
"And you ask yourself a: how people could leave the school system with those skills, and b: then how can they make their way not only into, but even out of, higher education with a degree."
Mr Schleicher said there needed to be a "more stringent" approach to quality assurance.
He continued: "It is also harder to do, how do you know what is the fault of the student and the fault of the system.
"It is a very complex system, but I do believe that a government that asks students to pay significant fees, should also have hard look at the quality of the services that are being provided to deliver for those fees.
"You can't put this on the shoulders of the students."
He further added that the evidence suggests people who are in jobs they are overqualified for is not down to a lack of graduate jobs.
"We would argue that actually the system is expandable, that employers are really looking for highly skilled people and if there would be more, there would be more good places for highly skilled people.
"Somewhere in the system, people have got a university degree without acquiring skills that you would hope they would have," said Mr Schleicher.
The report published on Tuesday made a number of other findings.
It is expected that 40% to 45% of the value of loans to higher education borrowers will not be paid back, with the public sector picking up the cost.
According to the OECD, at 70% England has the largest share of students benefiting from remission and/or forgiveness across the countries with available data.
The report also found that England has the highest tuition fees of all the OECD countries, except the United States.
However, despite the high fees, universities in the UK are still very attractive to international students.
In 2015, international students in the UK accounted for 18% of tertiary enrolment, behind only Luxembourg (47%) and New Zealand (20%) - and three times above OECD's average of 6%.
Education Secretary Damian Hinds said: "Since 2010 there are 1.9 million more children taught in good or outstanding schools, the attainment gap between rich and poor has shrunk by 10% and we have reformed qualifications to make them something parents, universities and employers can trust.
"The result of this is that, as the report recognises, we have high levels of young people in education or employment, the financial gains from going to university outstrip the cost and people are more likely to continue learning throughout their lives."