Nine out of 10 graduate work-experience interns are being illegally exploited by companies they work for, according to a top union adviser.

That is because many do not realise that firms have a legal obligation to pay at least the minimum wage, according to a survey.

Paul Sellers, a policy advisor for the Trades Union Congress (TUC), claims that this "abuse" of interns has been going on for years, particularly in the media industries.

He said: "In most cases, those undertaking work experience must be paid the minimum wage, and that is a bargain price for taking on graduates.

"Unions are gearing up to help the police in this area, and the TUC is this year calling on the Low Pay Commission to crack down on the abuse of work experience and internships."

He says that while "high quality work experience can be a great benefit to people just starting out their career, all too often employers are misusing their power to levy a toll of unpaid work on young people".

The poll reveals that some graduates work for a year without receiving any pay because employers quibble over the legal definition of the term 'worker', which implies a contract of employment rather than casual agreements.