Labour could tap wealthy graduates for the money to fund a £2.3billion annual scheme to fund free university places for the poorest students.
Bridget Phillipson, the shadow education secretary, has ruled out increasing student loans at a time of huge cost-of-living pressures.
But she left open the door to the return of maintenance grants that were scrapped by David Cameron.
She she that while the current system is 'not sustainable', it was possible to replace it with a more 'progressive' set-up 'without additional borrowing or spending'.
She is reported to have been referring to plans set out in May by a consultancy firm which suggested 'stepped' rates of interest paid by graduates on their loans, depending on their income.