With Labour having promised to scrap university tuition fees if elected, the Greens are going one step further, with a pledge to write off all existing student loan debts, at a cost of more than £14bn over the next parliament.

The party, which is already committed to ending tuition fees, concedes that this cost would be significantly higher over time, given the long period during which the loans are repaid.

However, the Greens argue that as well as releasing an excessive burden on young people, writing off the debt from the government-owned Student Loans Company would be notably less than it could be, given the expectation that little more than half the sums will be repaid anyway.

“The right thing to do would be to not only scrap tuition fees – a policy that we have already committed to – but also to write off the debt that students already have,” the Greens said in a statement.

“This would remove the weighty sack of debt they carry that holds them back from their aspirations – to have a secure home, pursue a career of their choosing, and to know that their education did not come at a price.”

Using estimates in March from the Office for Budget Responsibility, the party estimates that the policy would involve writing off £14.4bn in expected repayments over the five years of the next parliament.

The party briefing notes that with most loans paid back over many years – repayments are dependant on earnings – the overall cost would be much higher, adding: “However, this would be more difficult and uncertain to estimate.”

While there is no chance of the Greens forming the next government – they are standing in 467 seats but are unlikely to win more than one or perhaps two – the policy seeks to distinguish the party further from rivals on the left.

In 2014, the government said the proportion of loan sums expected to be written off was about 45%. The proportion of graduates failing to pay back loans was increasing due to the tripling of maximum tuition fees, low pay levels for young people and the increasing numbers who hold a degree.

The Greens are set to unveil their manifesto on Monday, when they say they will present the means by which they will pay for such plans, intended to include closing tax loopholes and increasing corporation tax.

Hannah Ellen Clare, co-chair of Young Greens, said: “This policy would seek to unlock the chain around graduates’ necks. There have not been many more farcical policies than student loans.

“The government pays them out and only ever gets back 55p in every £1, leaving a hole in their pocket and the pocket of students. It’s a one-way ticket to debt.”