More than £28m of over-payments on student loans in England are being held by the government, researchers have discovered.
It is the result of cases in which repayments continued to be taken even though loans had been paid off in full.
The Student Loans Company says it has tried to contact people who have been over-charged to arrange refunds.
The Department for Education says data sharing has recently been improved to prevent such over-payments.
The scale of over-payments sitting unclaimed has been revealed by Research Professional News, a publication for higher education.
They relate to money borrowed to cover tuition fees and living costs – with repayments deducted from graduates’ salaries each month.
Payments should stop when the debt has been cleared – but the research shows that for more than 510,000 students since 2009-10, there were extra deductions.
Freedom of Information requests showed almost £308m in over-payments, averaging about £600 per person.
Most of this was paid back – but £28.5m remains unclaimed and has stayed in the government’s coffers.
The biggest annual amount not refunded is from 2015-16, with £6.3m of over-payments still outstanding. From 2016-17, £5.9m of over-payments have not been paid back.
The Students Loan Company (SLC) says it has tried to “proactively contact all customers that have over-repaid”.
But it says contact details might be out of date and refunds will depend on these former students getting in touch.
“We want all customers to repay the right amount and not to over-repay,” an SLC spokesman said.
Claim a refund
Such over-payments should become less likely after changes introduced earlier this year, a Department for Education spokeswoman said.
This will allow weekly sharing of data between the SLC and Revenue & Customs, so that loan repayments and the clearing of balances can be updated more accurately.
In the past, such data sharing had been on an annual basis, which could mean a lag before the repayment system recognised the loan had been paid off.
“If a borrower believes there has been an over-repayment, they should contact the SLC to seek a refund,” the Department for Education spokeswoman added.