A small number of protesters from the National Campaign Against Fees and Cuts attempted to gain entry to the office of Mr Cable ¨C responsible for ÖйúAƬ as business secretary ¨C in his Twickenham constituency.

The group said it had also successfully occupied the office of John Hemming, Lib Dem MP for Birmingham Yardley, and targeted the Southwark and Bermondsey constituency office of Simon Hughes, the Lib Dem deputy leader.

In July this year, Lib Dem MP Danny Alexander, the chief secretary to the Treasury, told the House of Commons that the sale of pre-2012 income-contingent loans would raise ?10 billion and reduce the public debt.

Before that, in June, it was revealed that a government-commissioned study on the sale, conducted by investment bank Rothschild, included an option to increase interest rates for 3.6 million borrowers who took out student loans over the past 15 years.

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Increasing the amount that existing borrowers repay into the loans system would make the loans more attractive to prospective private buyers.

Another option suggested by Rothschild was for the government to continue to subsidise the loans after their sale to cover the risk posed to buyers by low interest rates on the scheme.

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Mr Cable ruled out asking existing borrowers to pay more as part of a sale, some time after the Rothschild story emerged.

However, today protesters left red boxes marked ¡°student debt¡± at the door of Mr Cable¡¯s office. The business secretary was not said to be present.

Hannah Webb, an NCAFC national committee member speaking from the protest, said protesters ¨C reportedly around a dozen - had ¡°got in [to the office] a little bit and then got moved out¡±.

Ms Webb, external affairs and campaigns officer at University College London Union, said the Lib Dems were ¡°very much leading on privatising the student loan book¡± and any sale would mean continued subsidy by the government when the loans were in private hands.

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She pointed out that Martin Wolf, the Financial Times columnist, has .

Ms Webb argued that any sale of the loans could mean ¡°changing the terms of repayment for students¡­which would just hit students and graduates even harder than they are already being¡±.

Asked whether the sale of loans is a low profile issue among students and graduates, Ms Webb said: ¡°It is not huge right now, but people are only just beginning to hear about it. The more people hear about it, the more people are totally appalled that it is happening.¡±

john.morgan@tsleducation.com