Lucy Fisher cites Sutton Trust research on unpaid internships in The Times.
Ministers are taking action to stop businesses employing unpaid interns, with HM Revenue & Customs establishing enforcement teams and issuing warnings to 550 companies about the practice.
The teams are expected to target media and arts businesses as well as professional services firms such as solicitors and accountants.
A fifth of graduates who undertake internships six months after leaving university find themselves in unpaid posts, according to the Sutton Trust charity. Minimum wage laws ban companies from offering unpaid internships but the government said there had been no prosecutions.
Businesses are directed not to avoid paying genuine workers by treating them as interns. However, volunteers do not require payment under the law and campaigners fear that employers are using this as a loophole.