At eight o’clock on a recent June morning, outside the University of London’s art deco Senate House, in Bloomsbury, a Latin American wake-up call is blasting away. Horns are blown, samba music bellows, empanadas and coffee are supplied, while the one-day strikers – among them cleaners, porters and receptionists – wave enthusiastically to the car drivers who honk support. This is protest as carnival.

The University of London employs a number of outsourcing companies. The strikers, who are striking under the slogan “Back in House”, want to become direct employees of the university on equal terms and conditions. Most are members of one of the country’s newest unions, the Independent Workers Union of Great Britain (IWGB), small but rapidly growing, established in 2012 and now with about 2,500 members. It has just constituted its eighth branch, the IWGB Electricians’ Workers branch.

It’s a gnat compared with giant unions such as Unison, which has 1.3 million members, but IWGB is attracting attention because it is beginning to carry a clout hugely disproportionate to its size. It is a non-bureaucratic, grassroots, “bottom-up” organisation. At a time when only one in five workers aged 25 to 34 are in a union, less than 14% of the private sector is unionised and the TUC general secretary, Frances O’Grady, concedes that the image of unions is “male, pale and stale”, IWGB is recruiting strongly from previously neglected, non-English-speaking immigrant workers. It is championing the rights of the lowest paid in the most precarious jobs, the young and those outsourced to private companies and in the gig economy. IWGB and its sister union United Voices of the World are taking on the multimillion-pound giants of the tech and app business world, such as Deliveroo, to win the most basic rights for their members – the minimum wage, sick pay and pensions. As the TUC celebrates its 150th anniversary, the IWGB could provide clues as to what the trade union movement as a whole needs to do – not just to survive, but to thrive.

Facebook Twitter Pinterest Jason Moyer-Lee. Photograph: Alicia Canter/The Guardian

At the Back in House strike is Liliana from Colombia, who became a cleaner at the University of London five years ago. Then, she was earning a little over £6 an hour, and says she was bullied by her supervisor. Now, she is paid the London living wage (£10.20 an hour). “I am not alone,” she says. “We have solidarity. They cannot make injustices against us because we stand together.”

The London university workers are far from alone in pushing for better working conditions. In a number of recent cases, huge, often global, employers are being forced to recognise the workers they claim are not employees. Last Thursday, 50 Deliveroo couriers won a six-figure payout because they had been denied rights including the legal minimum wage and paid holiday. A few days before, an employment tribunal ruled that 65 Hermes couriers, classed as “independent contractors”, supported by the GMB union, were entitled to the minimum wage, holiday pay and to reclaim unlawful deductions from their wages. Hermes is likely to appeal, citing inconsistency with previous decisions. The ruling could affect 14,500 of its couriers, some earning as little as £3.50 an hour. GMB’s general secretary, Tim Roache, said the decision was “another nail in the coffin of the exploitative bogus self-employment model, which is increasingly rife across the UK”.

The “bogus self-employment model” applies to a large proportion of IWGB’s members. Jason Moyer-Lee, 32, is general secretary. He heads a staff of 11, based in cramped offices in north London. All pitch in, employing an imaginative use of Google, Facebook and other social media, citizen journalism, community action, alliances with students and pro bono legal help. Finances come from sources such as crowdfunding and grants. Members pay £6 to £9 a month, far less than in larger unions, and the caseload of abuses is time-consuming and constant. Moyer-Lee, an American, has an astute knowledge of the law, and a robust approach.

Almost a year ago, the chief executive of the Royal Society of Arts, Matthew Taylor, published a long-anticipated, government-commissioned report that many gig-economy workers had hoped would be a turning point in their battle for better working conditions. The report made 50 recommendations, but despite this received a lukewarm response. Moyer-Lee, along with many other critics, believes it was nowhere near bold enough and let the government off the hook.

In more than 60 pages, Moyer-Lee published his response to the report, dismissing it as “fluff” and a misunderstanding of the law. “For the most part, the law does give rights,” he says. “But some companies are unlawfully able to deprive people of those rights because the law is not enforced.”

Facebook Twitter Pinterest Senate House, University of London. Photograph: Alamy

Moyer-Lee first got in touch with low-paid, predominantly Latin American cleaners and porters while completing his PhD at the University of London in 2011. A Spanish speaker, he initially volunteered as a translator and taught English, eventually helping at the university’s Senate House Unison branch.

“The branch had only 20 outsourced workers. We spoke Spanish. We recruited, and membership rose to 100,” Moyer-Lee says. “It’s about working from the bottom up.”

In 2011, cleaners and porters, supported by students, held the first wildcat strike over problems with unpaid wages involving services group Balfour Beatty WorkPlace. “It was an issue of incompetence,” he says.

Collective action led to 17 workers receiving £6,000 in pay that was owed. A battle to secure the London living wage was also successful and was rapidly followed in September 2012 with the launch of the 3Cosas (Three Things) campaign to gain closer parity with in-house staff on sick pay, pensions and holidays.

Fourteen months later, after demonstrations, student sit-ins, strikes, copious use of social media and 1,400 emails sent by members of the public to the vice-chancellor, 3Cosas was successful. The strikers received a pay rise, entitlement to six months’ sick pay and five days’ extra holiday. However, Moyer-Lee says, while Unison nationally fights hard for the lower paid, at a branch level the 3Cosas campaign met with resistance. In spring 2013, a number of Unison members broke away and founded the University of London branch of IWGB.

“Unison didn’t want to upset the bosses and rock the boat,” Moyer-Lee says. “For us, it’s about disruptive surprise protests, direct action, mini-occupations and exerting as much public pressure as possible until it becomes better for the university to give in rather than risk continuing reputational damage.”

That risk is a strong lever. Two weeks ago, the university’s central administration, having spent more than £415,000 on security around the Back in House campaign, issued a statement confirming that some outsourced workers would be brought in-house, with all zero-hours contracts ended by the summer. It told the Observer: “Nevertheless … the university will not commit to unrealistic and undeliverable time-frames.” This vagueness, IWGB says, means the protest continues. “All our outsourced workers must be brought in-house within 12 months,” says Moyer-Lee. “That’s our goal. We have public support.”

Building public support often comes from Twitter, one of IWGB’s favourite pulpits. Glen Jacques, an IWGB member, recently posted that he had been a receptionist at London university for 14 years. Twelve years ago his job was outsourced to facilities management group OCS and he lost his pension rights. Then came other such groups – Balfour Beatty WorkPlace, then Engie and now Cordant. Initially, Jacques writes, he was proud to be part of a prestigious university but now, he warns: “Every pyramid is only as strong as its foundation, and if the foundation is not maintained to a high standard, the pyramid will, in time, collapse.”

Outsourcing, agency work, zero-hours contracts and the conditions revealed, for instance, at Sports Direct finally prompted a government response last year. Theresa May said she would ensure “all work is fair and decent” – a promise, so far, housed in the mausoleum that contains many of her good intentions. No major legislation has been announced.

“This isn’t just about the gig economy. All business is going more and more digital, leaner and leaner,” says Mags Dewhurst, part-time bicycle courier and vice-president of IWGB. “Next, it will be banking and retail. These bad practices have to be stopped now.”

Two months ago, the breathtaking scale of employment rights abuses was revealed in the first strategy report published by Professor Sir David Metcalf, the director of labour market enforcement, who reports to both the home and business secretaries.

Unpaid wages in 2016 amounted to a staggering £3.1bn; incredibly there is no regulator to ensure holiday pay is given, so “wages theft” of £4.5bn – 15% of the industry – is misappropriated from agency workers annually. In addition, the Employment Agency Standards Inspectorate has only nine inspectors overseeing 18,000 employment agencies, and there have been only 14 prosecutions for non-payment of the minimum wage since 1999. But there are wins.

IWGB has recently successfully brought several employment tribunal test cases around the issue of what’s called “worker status”. Moyer-Lee’s demand is that the correct legal label is applied to current working practices. In general, as in the Hermes case, if couriers and private hire car drivers, for instance, work for another business and not for themselves, in law, they are part of a sub-category of the self-employed called a “limb (b) worker” (under the 1996 Employment Rights Act). They are self-employed but entitled to “worker” status that includes trade union rights, a minimum wage, paid holidays, automatic employer pension contributions and protection from discrimination.

“Judges are not saying these cases are murky areas. Their judgments are excoriating and extremely critical of the companies,” Moyer-Lee says.

Another of IWGB’s effective tactics is to target the clients of gig businesses. “In the case of eCourier, the CEO made an offer, we rejected it,” Moyer-Lee explains. “We emailed his clients constantly. Four gave the CEO an ultimatum to do something about his business model. The couriers received, on average, a 28% pay increase.

“Companies will argue that the law is confusing,” he adds. “The law is clear and many companies are on the wrong side of it. The companies know exactly what they are doing – it’s their core business model.”

A similar spotlight of unwanted publicity has been shone on Deliveroo. IWGB is fighting the food delivery company for the human right of its drivers to collective bargaining. A win could upend yet another major player in the gig economy.

A crowdfunding campaign to raise £50,000 to fight the case attracted donations of £9,000 within hours. Commenting on paying riders as workers with employment rights, Will Shu, co-founder of Deliveroo, said: “It’s not a cost thing … the whole point is flexibility. It’s what people sign up for.”

Moyer-Lee points out: “Flexibility does not need to come at the expense of employment rights.

“The main problem with the so-called gig economy is that existing law is not enforced,” he adds emphatically. “An agency or government department is needed that has the mandate and the resources to look at an employer’s operation, build a case, prosecute and impose severe sanctions. That’s fair – and that is what we don’t yet have.”

Workers who run their union

Mags Dewhurst, 30

Facebook Twitter Pinterest Mags Dewhurst. Photograph: Richard Saker/The Observer

Part-time bicycle courier and vice-president of IWGB

“Most bicycle couriers cycle 50 miles a day, five days a week. On average, they do two and a half ‘drops’ [of packages] an hour. It’s hard on the body and hard on the bike. It’s a price war between the companies, which are reducing prices to win contracts, so it’s the couriers who take a bigger and bigger hit with longer hours and less and less money. Let’s call outsourcing what it is – a way to drive down costs.

“When we protested three years ago [and subsequently received a pay rise] we occupied receptions, had banners and banged noisy drums. Most bosses had never seen a courier before. We are invisible. Now, since the pay rise, it’s better but the fight goes on. It’s the best job I’ve ever had but what also matters is a decent wage, parity and respect.”

Sarah Anderson, 59

Facebook Twitter Pinterest Sarah Anderson. Photograph: Martin Godwin/The Guardian

Chair of the first foster care workers’ branch of IWGB (left)

“I’ve been a foster care worker for 10 years. I have a degree in counselling therapy and worked with excellent adolescent mental health teams in the NHS. Two months after I became a foster care worker, I couldn’t believe I was being treated so badly.

“We nurture the children and young people but this is also a job. We tick all the worker-status boxes, yet we have no employment rights, no holiday pay, and 50% of foster care workers are given less than £100 a week, which hardly covers the basic needs of the children in their care.

“Foster care work is the only trade where the regulator and the employer are the same entity. A local authority or a private agency employs us directly, and directs everything we do with a child.

“I’m waiting to go to a tribunal to win worker status. None of us has been in a union before but we have to make a stand. It’s about fairness and rights.”

Henry Chango Lopez, 39

Facebook Twitter Pinterest Henry Chango Lopez. Photograph: Katherine Anne Rose/The Observer

A porter at the University of London for eight years and, since February, the full-time president of IWGB (above)

“I came from Ecuador 18 years ago. When we began the fight in 2010, I was on £6.90 an hour. We had a wildcat strike because some of us hadn’t been paid for two months.

“We had to educate the workers that they have no less rights than anyone else in this country. After the 3Cosas campaign, we won the right to six months’ sick pay and five days’ more holiday, which meant it was possible for some of us to go back home for a holiday.

“The University of London has said it will bring some outsourced workers in-house, but that’s too vague. We are fighting for all the workers. We have a lot of public support. I think we are very close to being victorious.”