Danny Alexander, the Chief Secretary to the Treasury, has confirmed that the Government will be privatising student loans as part of a plan to raise £15bn from sales of public assets, in order to boost investment.

Speaking to the Commons today, he said:

We will take action to sell off £15 billion worth of public assets by 2020. £10billion of that money will come from corporate and financial assets like the student loan book. And the other £5 billion will come from land and property. Mr Speaker, government is the custodian of the taxpayers’ assets. When we no longer need them, we should sell them back at a fair price – not act like a compulsive hoarder.

The sale is not expected to be finalised until 2015, two years later than originally planned.

In order to get a decent amount for the loan book, the government is expected to offer sweeteners to whoever purchases it. The most extreme of these would be the proposal, revealed earlier this month, to lift the cap on interest paid by people who took out loans between 1998 and 2012.

That change would increase the revenue for whoever owned the loan book in 20 to 30 years time, because people who would otherwise have paid their loans off will still owe money. But it won't do anything for the government's balance sheet today – unless the government sells the book to a private company for a lump sum, which is exactly what it plans to do.

Another sweetener proposed has been what is called a "synthetic hedge". That would involve artificially replicating the change, by promising whoever buys the student loans that they will be paid the difference between the actual cash flow and the estimated cash flow which would have been received without the cap. It's fairer – because it spreads the cost throughout all taxpayers, rather than lumping it on young graduates – but it's also far more cowardly. Crucially, because the government would't have to pay any extra cash flow now, it won't have to work out where that extra revenue comes from. That's a difficulty it gets to offload onto a future government.

Whatever happens, a sweetener of sorts will have to be offered. Student loans are a classic example of an asset which is worth far more to the government than any private entity: a revenue stream spread over decades, with a high degree of variability in the value of the repayments.

For an organisation, like the UK state, which can borrow at record-low interest rates for decades on end, selling it off at a discount to secure a cash lump sum now is terrible financial management. It is as though they had decided borrowing to invest was a good thing, but they'd rather pay higher interest rates than they have to in order to keep it off the books. Surely not…