Inflexible course design and a lack of good quality information, advice and guidance are also said to be factors in the decline in part-time students, according to a collection of essays published by the Higher Education Policy Institute (HEPI).
The organisation said the essays explain the "catastrophic" fall in part-time student numbers, which it says is harming the economy and limiting people's ability to transform their lives.
The publication - It's The Finance, Stupid! The Decline Of Part-time Higher Education And What To Do About It - also proposes options for tackling the problem.
It suggests cost-effective changes to the funding rules, such as providing support for second-chance students and providing funding for students taking a module or two rather than a full course.
Another proposed solution is to engage employers in course delivery and give Local Enterprise Partnerships a more formal role.
In his foreword to the publication, Nick Hillman, the director of HEPI, wrote: "The collapse in part-time study is arguably the single biggest problem facing higher education at the moment.
"There are other challenges too, such as the future of the research environment, how to assess the quality of teaching and dealing with the effects of marketisation. But it is the fall in part-time learning that is probably the biggest black spot.
"The fall in part-time student numbers is clearly partly - possibly mainly - associated with the changes to student finance, hence the title of this collection.
"Part-time numbers have fallen more in England than other parts of the UK with lower (or no) fees, but it is not the sole cause. The decline began before the £9,000 fees were introduced.
"Any solution is likely to rest upon innovative delivery methods and other ways of improving access as much as relying on tweaks to the entitlement for financial support."
Peter Horrocks, the vice-chancellor of The Open University and the author of the opening chapter, said: "For too long the focus of higher education policy has been on the traditional university route of school leavers heading into full-time study.
"As this collection shows, part-time higher education has a key role to play in boosting productivity, contributing to economic growth and driving social mobility.
"Alongside our calls for the reversal of the policy to refuse loans for most second degrees, this paper is full of proposals which, if taken seriously, would help the Government deliver on its promise to support the most aspirational people in our society."
Contributors to the publication came from organisations including the National Union of Students, The Open University, the Workers' Educational Association, and the universities of Cambridge, Northampton and Wolverhampton.