In Britain, in 2014, we are compelled to debate whether people should work for free. Unpaid internships have become a pillar of the modern British class system, discriminating on the basis of wealth rather than talent. The system acts as a filter for entire professions, helping to transform them into closed shops for the uber-privileged. Not only are they exploitative, they effectively allow the children of the well-to-do to buy up positions in the upper echelons of British society. But, finally, it is possible – just possible – that this key means of rigging Britain in favour of a small elite faces its reckoning. On Tuesday, Labour shadow minister Liam Byrne will return to his old school to set out the case for dealing with this national scandal. Despite some internal resistance, Labour’s leadership are moving towards backing a four-week limit on unpaid internships.

According to the Sutton Trust, more than one in three graduate interns are working for nothing. At any given time, the charity estimates, 21,000 are working unpaid, although a 2010 estimate by the thinktank IPPR put the figure at 100,000. For those unable to rely on the Bank of Mum and Dad, such unabashed exploitation can be completely unaffordable. Unpaid internships are often gateways to professions – like, for example, law, the media, the tragically professionalised political world – and are all too frequently located in London, one of the most expensive cities on Earth. The Sutton Trust estimates that a single person in London will have to cough up £5,556 for the privilege of undertaking an unpaid internship for six months; in Manchester it is not much cheaper, at £4,728.

For a generation facing a worse lot in life than their parents, this is a time of desperation. Hundreds of thousands of young people are out of work; many others have been driven into insecure or zero-hour employment; and around half of recent graduates are trapped in non-graduate work. Such desperation is lucrative for many employers. They know that those with the means will do whatever they can to get their foot in a door which has been slammed in the faces of so many others. After all, more than half of employers surveyed refuse to give jobs to graduates with no prior work experience.

The public has little doubt that unpaid internships are a wealth bar. According to polling by the Social Mobility and Child Poverty Commission, 74% of Britons believe that a young person in their family could not afford to take up an unpaid internship. Yes, there are many reasons why the apex of society is such a stitch-up for the pampered and privileged, but the internship filter is certainly one of them. More than half of the top 100 media professionals attended a fee-paying school, even though just 7% of Britons overall did; and 43% of newspaper columnists were educated in the private sector. This is not just an unjust waste of talent, leaving aspiring journalists from more humble backgrounds unable to pursue their dream. It helps to ensure that the media reflects the opinions, prejudices and priorities of a gilded elite.

Many unpaid interns wish to remain anonymous out of a fear of damaging their careers, but their experiences are telling. Take one woman who won a month-long internship with a leading Sunday newspaper. “Because the internship was unpaid and I’m from Leicester, not Chelsea, I could only afford to stay for one week and got very little out of it,” she says. She now works in press management. Freddie Foot from Bristol recently graduated with an international development degree. “The current climate seems to imply that to get your foot in the door you have to do one of these internships,” he says. “The issue is that unless your parents live in London – where most of these jobs are – or you can take three months off unpaid, it is basically an impossibility.”

When Matthew Cole moved to London, he lived in a “makeshift DIY bedroom partition in a lounge” in a building that should have been condemned, and worked to try to support his unpaid labour. “However, when you are exhausted by the work you do to pay the rent and eat, it’s very hard to find the energy or time to work for free on anything, internship or otherwise.”

Apologists for unpaid internships – proof that you can find people who will defend almost anything – sometimes mount the following defence: if the non-privileged are real go-getters, they will spend their every remaining hour slogging away in bar jobs to support themselves. What a society they condone, where those without money must work themselves half to death in order to even be considered for a job in an top profession.

These unpaid internships should be illegal – and by that, I mean under existing law. As Intern Aware, a group that has done more than anybody to fight this national scourge, point out, under employment law if you “work set hours, do set tasks and contribute value to an organisation” you are a worker and are entitled to a minimum wage. And yet a YouGov survey found more than eight out of 10 businesses who used unpaid interns admitted they undertook useful tasks.

HMRC, the department responsible for enforcing the law, has been “totally ineffective”, says Intern Aware’s Ben Lyons. So it took matters into its own hands, encouraging former unpaid interns to take their employers to court to recoup wages they should have been paid. Ex-interns from Harrods, Sony and a leading London tourist attraction are among those who were successful. Such cases serve as useful warnings, but they are no solution. “If the primary reason you’re doing an internship is to get a reference or get a new job, you won’t do that,” says Lyons. “There’s no real way under the existing law that the vast majority of internships will come forward.”

Change may now be afoot, however. As well as a hardening of the Labour line on internships, this debate is coming to the House of Lords – with some cross-party support for reform. There are other battles that must be fought: expensive post-graduate qualifications are now often a must for many often a must for professions but too costly for many; there’s a need for scholarships to support those from underrepresented backgrounds; and we have to tackle the social and economic inequality that lies at the root of the gap in educational attainment.

Yet a curbing of unpaid internships would be a real blow to Britain’s entrenched class system. What an opportunity: it must not be missed.