Government plans to expand higher education by getting employers to "co-fund" degree courses in England are risky, a think tank has said.
Foundation degrees are designed in close co-operation with employers
A report by the Higher Education Policy Institute (Hepi) says the potential market for such degrees is untested.
It says expanding them at a reduced rate of state funding risks repeating the underfunded growth of the 1990s.
Meanwhile ministers have defended their plans to allow colleges to award vocational foundation degrees.
The Hepi report focuses on the government-commissioned study by Lord Leitch into the UK's skills needs.
It queries his "hugely ambitious" target of having 45% of those aged 19 to 65 educated to degree level by 2020.
It says the increase would have to come from people over 30, whose participation tends to be almost exclusively part-time.
Leitch argues that employers should influence or even determine what universities offer.
But this would mean a move away from student demand being the main thing that determines what courses universities offer.
"There is a risk that what employers want will often not be what students want - especially where courses depend on attracting students who are not employees of an employer-customer.
"This process can be taken only so far."
Report authors Tom Sastry and Bahram Bekhradnia say the current policy agenda is also about trying to persuade employers to contribute financially.
It appears that what is envisaged is the use of employer contributions to part-finance the further expansion of higher education.
A letter to universities from the Higher Education Funding Council for England said it was providing for them to deliver the equivalent of 5,000 more full-time students, "the contribution from employers making up around half the cost of delivery".
They argue for a new "golden rule": "the scale of the government's ambition for employer-funded education and training should be determined by real evidence of employer demand".
"It would be quite wrong to divert funding from provision which is meeting a need to provision for which no need can be demonstrated."
Employer-designed and funded two-year foundation degree students currently make up just 0.4% of the total number of new students each year.
"If foundation degrees with their focus upon employer requirements are supposed to herald a new age of employer-funded higher education, something very large has to emerge from what - at present - is a very small acorn."
Further education debate
What is more, these degrees largely replace old HNDs. So there is little evidence of additional student demand for such courses.
Nevertheless the government is committed to their expansion, and the Further Education and Training Bill proposes to let further education colleges award them.
As the bill was given its second reading in the Commons on Monday night, the Liberal Democrat spokeswoman Sarah Teather said this "most controversial" idea "appeared from nowhere without consultation with FE colleges".
The Further Education Minister, Bill Rammell, said: "I am pleased that HEPI conclude that government is right 'to pursue vigorously' the prospect of tempting employers to invest directly in higher education. We are not moving to employer-led demand at the expense of student demand - we?re doing both."
Mr Rammell said that to encourage more people into higher education "we therefore need to refocus some - but not all - of the higher education sector to widen participation amongst older people".
The Tories complained that the bill involved "yet another" expensive round of reorganisation of the sector, but the government said it would result in savings.