Here are two things you probably know. First, huge swaths of Britain’s workforce aren’t paid enough to live on and rely on benefits to get by. Second, there’s sod all chance of this changing. David Cameron’s hardly likely to take on business, the trade unions get punier by the day and work is becoming so insecure that those doing it dare not challenge their bosses.

As I say, you know this, perhaps even while deploring it. Contemporary Britain treats its workers mean, keeps its house prices inflated and lets the rich stash their cash in whatever bolthole they please. To all of which, let me make one small qualification: watch a woman called Maggie Dewhurst. Together with her colleagues, she’s begun a fight that might just upend an entire rotten system.

I met Dewhurst last Friday, the same day the minimum wage shot up. This, you’ll remember, emboldened George Osborne to claim the Tories were the “workers’ party”. Except Dewhurst isn’t entitled to minimum wage. Nor does she get sick pay or pretty much any other form of protection most employees take for granted – even though she works four long days each week as a cycle courier delivering urgent medical supplies to hospitals around London.

Dewhurst’s firm classes her and all its other couriers as self-employed “independent contractors”. That’s what the fight is about – and it’s one that could prove crucial not just to couriers, but to all those who want a fairer jobs market.

One of the big stories of post-crash Britain has been the large rise in the numbers of self-employed people, who now make up one in seven of all workers. If you’re a minister, you consider this great news – indeed, it’s one of the most important reasons for those low jobless figures that come out month after month. No wonder David Cameron talks of his “huge respect” for those striking out on their own. No wonder Nick Clegg boasted before the last election that “if you want a glimpse of the sort of worker that will thrive in the new economy, you need look no further than the growing numbers of self-employed people”.

If you believe that, you too are the sort of gull who can march a party out of government and into electoral oblivion. Because if there’s one thing we know about the 4.8 million self-employed it is that lots aren’t thriving at all. Sure, some may be the Bransons and Sir Alans of tomorrow – but about half are low paid.

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The world in which Dewhurst lives, the world of self-employment, is for political and economic purposes almost subterranean. Everyone knows it’s big and important; hardly anyone’s studied it. But of what little we do know, rather a lot is worrying. Take the recent survey by Citizens Advice of self-employed people who had contacted it: it found that more than one in 10 would probably be classed by a court as employees, with all the extra pay and rights that status brings. Trade unionists say they have noticed a growing number of industries shunting workers into self-employment: cut-price gyms, pest-control outfits, car washes, even call centres.

Last week, the Financial Times reported on a conference this year for Best Western hoteliers at which two lawyers advised attendees on coping with the new higher minimum wage. A key suggestion was to consider “facets of your business which could be staffed by self-employed people”.

In each of these cases, the nature of the work or the basic relationship between boss and worker may not have changed. But the risk is that through lower wages and more overheads, the companies are redefining their workforces into poverty and precarity.

Which brings us back to Dewhurst. Under law, independent contractors forgo their employment rights for greater freedoms: they can refuse work, set their own hours and subcontract jobs to others. Working for the largest courier firm in the country, CitySprint, Dewhurst points out that she can’t do any of that. She wears a uniform with a logo, clocks in with her controllers each morning and a handheld electronic device communicates which jobs she does next. “For 50 hours each week, I’m told what to do,” she says. CitySprint described this to me as “smart scheduling, to ensure [couriers] can maximise their earning potential”.

If a new member of staff does the jobs in what the controllers deem the wrong order they get told off. If they go “too slowly” they get told off. If she wants to go on unpaid holiday, her controllers have to OK it. If on the other hand a courier gets sick or is involved in an accident, the company can just drop them. Dewhurst recalls a colleague at another firm who had fallen off, smashing his shoulder. It was a big injury, and the doctors thought he would need months off. Her mate couldn’t afford to go more than seven weeks without work – and went back without having properly healed. And when he went back, his controller told him: “You’re not as fast as you used to be.”

To duck out of paying staff more, companies are redefining their workforces into poverty and precarity

This is freedom: the freedom to be controlled and abused. And underpaid. Couriers are paid by the number of jobs, not hours – but Dewhurst has done a pay audit of two of the big firms in the industry and found evidence that many workers are paid below minimum wage.

Dewhurst and her colleagues in the Independent Workers of Great Britain (IWGB) union are taking some of the biggest courier firms to an employment tribunal. They’re not alone in doing this: drivers for Uber are also taking the cab firm to a tribunal this June. In both cases, workers will argue that, despite Uber claiming that they benefit from being able to “work completely flexibly”, their status as “independent contractors” is a sham and that they should get guaranteed pay and protection. If they win, it will send shockwaves through both the cab and the courier industries – and many other businesses that use self-employment. Neither CitySprint nor eCourier would comment on the tribunal claim.

It’s not an even fight, I’ll admit. On the one hand, a tiny union; on the other a £1.7bn industry. Even if Dewhurst and the other activists win the tribunal, they should be ready for this to go all the way to the supreme court. But I’ve seen the IWGB win other seemingly impossible fights with the same canny mix of tough demands, direct protest and willingness to keep pushing. They’re going after some of the trickiest and most important targets in British capitalism: the businesses that make billions out of outsourcing contracts and cheap labour. Their first tribunal is at the end of June. Anyone who believes that businesses should work as honestly as their workers has got to be cheering for Dewhurst and her colleagues.