The soaring price of tuition fees has been blamed for the "collapse" of part-time education.
The Higher Education Policy Institute (HEPI) said there had been a "catastrophic" fall in numbers, which it claimed is harming the economy and limiting the opportunities for people to switch careers or improve their skills.
HEPI director Nick Hillman said other factors such as poor teaching methods and availability of courses may also play a part, as the decline began before the £9,000-a-year fees were introduced.
Possible solutions in the report, entitled It's The Finance, Stupid! The Decline Of Part-time Higher Education And What To Do About It, include changes to the funding rules - such as providing support to second-chance students, and funding options for those taking a module or two instead of a full course.