Universities Minister Jo Johnson has announced the sale of £4 billion of student loans owned by some 450,000 people.

The sale of the loans, which entered repayment between 2002 and 2006, is the first in an intended tranche of sales over the next four years of loans made before 2012. The combined sales are expected to raise £12 billion for the exchequer.

The government has promised that the sale will not entail any alteration of the terms and conditions of the loans, nor of their repayment scheme. The loans will continue to be administered by the Student Loans Company.

In a statement, Johnson said: “This sale will have no impact on people with student loans and will only proceed once we are satisfied that it represents value for money for the taxpayer.”

However, critics of the move argue that the government has previously manipulated the terms of student loans to their own advantage. Particularly contentious has been the decision to freeze the repayment threshold on student loans, which means that repayments have effectively grown in size as inflation has increased. The government’s policy of attaching the calculation of the interest rate on student loans to the rate of RPI in March of each year resulted in an increase of three-quarters in student loan repayments in 2016.

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The NUS has condemned the move, its Vice-President (Higher Education) Sorana Vieru calling it “economic illiteracy” and “privatisation through the back door.”

She argued that “bankers” should not “profit on the backs of graduates who took out loans because they had no other option.”

She added: “If it becomes the norm for student loans to be sold to private investors, rather than held by government, it will be all the more tempting for governments to subject future students to extortionate interest, commercial terms and conditions and the raising of the repayment threshold, making loans even more attractive to private interests, but all the harder for new graduates to economically contribute to society.”

Sally Hunt, the General Secretary of university workers’ union the University and College Union (UCU) also criticised the government’s plans. She said: “The government has tried to sell off parts of the student loan book before, but not gone through with it because it didn’t feel the taxpayer would get a good deal.

“You can forgive our scepticism when the minister [Johnson] says people with student debts have nothing to fear.”

The government has previously sold quantities of other, mortgage-style student loans, but this is the first sale of the loans whose repayment is reliant on their holders’ income exceeding a set level