The 38-year-old single mother may eventually pay it off, when she starts teaching in two years’ time. But it seems future women teachers, starting university in 2006 when student fees could rise to pound;3,000 a year, may never get back in the black.

Research carried out for the Liberal Democrats shows debt will hit female recruitment to all the public services, including teaching. Women, with the exception of those in secondary shortage subjects, for whom the Government is repaying student debt, could owe still pound;20,000, 28 years after graduating.

Mrs Smith is already trying to move from primary into secondary English teaching, to benefit from the shortage subject initiative.

The former mortgage manager said: “I have always wanted to be a teacher, but that amount of debt would have made me think twice now about going for a degree and teacher training.”

The Lib Dems estimate that students starting in 2006 will graduate with pound;21,000 of debt. Men will be in the black by the age of 44. But women, who start on lower salaries and earn less, will never keep up with the interest on the debt.

Phil Willis, the party’s education spokesman, said: “Even with the salaries teachers now earn, the majority of women primary teachers will never pay off their loans.”