It is not school-leavers, but those aged over 19, especially lone parents and couples with children who need extra cash, says an in-depth study of 1,000 students in 80 colleges.

Professor Claire Callender of South Bank University found that older students earn on average three times as much as the 16 to 17-year-olds (pound;6,929 a year compared with pound;2,202), but this was more than outweighed by family, housing and other commitments.

Not surprisingly, their struggle to survive and support families while studying is reflected in their relatively poor academic performance, limited participation in college life and tendency to drop out, her study found.

Raw figures for student spending sometimes mask real needs. The average student’s income is pound;5,192. But younger students are far more likely to be able to call on parental or family contributions.

Similarly, Callender finds that food and drink costs are twice as high for older students (pound;2,408 against pound;1,094 for the under-20s).

“This does not mean they eat twice as much or more expensively,” she says. “To understand this discrepancy we have to examine the older students’ living arrangements and family circumstances.”

Housing costs, rent and bills largely account for the differences in students’ spending. Older students are more likely to live on their own or with partners, while nearly all 16 to 18-year-olds were based at their parents’ home and paying no rent or household bills.