Online reviews for this small south-London nail bar are mixed. “Best nail bar in Peckham,” one says. Most comments, however, are more grudging. “Suppose you get what you pay for,” another concludes (customers here do not pay very much, just £10 for a full manicure). Most telling are the comments about the staff. “The younger girls and boys seem to be learning as they go”; “Communication is close to none as they don’t speak English.”

It is this lack of English that is one of the warning flags that has put the shop on a list of nail bars requiring investigation for possible exploitation. On a slow Thursday afternoon, the shabby venue is being raided by 20 police officers; three people are later arrested on human trafficking charges and four frightened young employees are taken temporarily to a council-run reception centre, where they are given medical treatment and advice.

Cut-price nail bars have become a cornerstone of the high street, flourishing as more established shops close. In the past 20 years, manicures have gone from being an extravagant luxury mostly enjoyed by a moneyed elite to an affordable treat, easily accessible to everyone. But the public awareness of what the low costs may mean for those who work there remains hazy. It is easier to associate cannabis farms and brothels with exploitation. Operating in plain sight, nail bars seem more improbable fronts for modern slavery; it is very hard to link such an innocuous service with such serious crimes.

Kevin Hyland, the UK’s first anti-slavery commissioner, who stepped down in 2018, says people remain confused about the presence of exploitation on the high street because they expect trafficking to be hidden. “People see the shops, they’ve been there for years, police cars drive past them, the local authority collects their rubbish, so they assume they can’t be one of the places where modern slavery happens – an offence that carries a maximum penalty of life imprisonment.” Familiarity can also add a sense of respectability to the premises. “The longer the shop has been there, the more accepted it is,” he says.

Unease about the treatment of vulnerable young Vietnamese people in the UK manicure industry, however, has been slowly rising over the past decade. Then, in October, 39 Vietnamese people were found dead in the back of a refrigerated lorry in Essex. Ten were teenagers. Pham Thi Tra My had texted her mother from the lorry: “I’m sorry Mum. My journey abroad hasn’t succeeded. Mum, I love you so much! I’m dying because I can’t breathe.” Anti-trafficking experts believe that they were brought in to the country to work in nail bars, restaurants and cannabis farms. Southwark council has been working with the Metropolitan police on inspecting nail bars since last summer, and the operations have been stepped up in the wake of the Essex tragedy. Yet even news of these deaths has done little to dampen customers’ enthusiasm for £10 manicures.

The venue in Peckham is one of five in Southwark being raided simultaneously by 100 police officers. The shop’s thin veneer of frivolity is rapidly stripped away. Inside, there is confusion as eight of the 20 officers crowd inside the narrow space between a row of battered, mismatched treatment chairs, where two startled customers are having their nails painted, and a wall lined with rainbow-coloured pots of varnish. “This is a search warrant giving police the authority to search these premises for evidence of human trafficking,” one of the officers announces. The customers hurriedly leave, while police begin attempting to interview the seven members of staff, all of them Vietnamese.

Unravelling who is a victim and who might be exploiting them in this kind of scenario is not always easy. And in this operation it is hampered by a decision to allocate just one interpreter to the 25-strong team of police, social workers, immigration officers and council staff squeezed inside the shop and gathering on the pavement outside.

The nail-bar workers, who are told by the translator they face questioning, look alarmed, but say nothing. By the window, a boy in a grey top, clearly a teenager, sits on a swivel chair, his hands pressed anxiously between his legs, his feet not quite touching the floor. With the translator elsewhere, two social workers try without success to speak to him.

“How old are you? How old are you? You don’t know how old you are? Your age?” one asks, using the time-honoured British technique of communicating with a non-English speaker, of slowly repeating the same question, louder and louder. He replies quietly in Vietnamese, looking unhappy. “How old are you? Do you speak English? I can’t get anything out of him,” she says, with unreasonable irritation.

A teenage girl, who, like all the staff, is wearing a grey top, tells officers through the interpreter that she is 17, but says she isn’t actually working in the shop, and has just stopped by to say hello to a friend as she was in the neighbourhood. “Are your parents here? You mum or dad?” a police officer asks. She shakes her head.

The only adult man among the staff is very agitated, and repeatedly requests to be allowed to go to the toilet. Police refuse, concerned that he wants to get rid of something incriminating. Instead, he sits gloomily, snipping his nails, dropping the clippings on the floor. An older woman says she is worried about her baby at home, and asks to leave, but she is told that no one can go until checks have been made on everyone’s immigration status; she is later arrested. One of the younger women says all the takings (the nail bar accepts only cash) are put in a drawer until the end of the day; no one will give a clear answer about how, or how much, they are paid.

Figures released last month suggest that the government’s determination to crack down on modern slavery is failing, with only 42 convictions on slavery and human trafficking in 2018, down from 59 in 2017 and 69 in 2016 – despite the fact that 6,993 potential victims were identified in 2018, a 36% rise on 2017. Theresa May introduced legislation to combat modern slavery in 2015, describing it as one of the “great human rights issues of our time”. There was scepticism from some about whether this concern about human trafficking was just the acceptable face of the government’s preoccupation with cutting net migration numbers, and creating a hostile environment for illegal immigration, but most charities welcomed the initiative. However, since then there has been disappointment about the lack of funding for implementing its measures. There have been very few successful prosecutions of nail-bar owners. In the only high-profile case, two years ago, four teenage girls were found to have been trafficked from Vietnam, forced to work without pay and made to sleep in a loft above Nail Deluxe in central Bath. Police frequently state that victims are too frightened to give evidence against traffickers, but on the evidence of the Southwark operation, their reticence may sometimes simply be down to insufficient interpreters.

Outside the shop, more police officers are questioning a tired-looking Vietnamese man who has been peering through the back of the building, then watching proceedings from the other side of the high street and making calls. They ask him to hand over and unlock his phone.

“It’s not my phone,” he tells them, speaking Vietnamese to the translator. “Some lady just gave it to me.”

“Can you just tell him I’ve never heard such rubbish in my life,” the police officer says, holding the phone in front of the man’s face to see if it would unlock with facial recognition.

“Tell him we are going to arrest him on suspicion of theft of a mobile phone.” The man unlocks his phone and officers look through the 20 calls he has made and received during the 45 minutes since the raid began, establishes that a number of calls have been made to staff inside the shop and decide to arrest him on suspicion of involvement in modern slavery and people trafficking.

Shortly, another man comes to the shop, pushing a small baby in a pram, and looks through the windows at the staff inside. “Is this your shop?” police ask him. He shakes his head, but when asked to show ID, police recognise him as the man named as the shop’s manager on a notice inside. Another officer takes the pram, handcuffs him and tells him: “You are under arrest for arranging and facilitating modern slavery. We’ll look after the baby, don’t worry.”

The mother of the baby has already been taken from the shop to a waiting police car. “He’s been nicked; she’s been nicked. Do we bring the baby to the police station?”

“We don’t want that. We’ll have to take her into care.”

Beneath the pram’s plastic rain cover, the baby peeps out, waving its arms around peacefully.

“Is there anyone else who can look after the baby?” a police officer asks the translator to ask the man, adding in an aside: “We’re getting our money’s worth out of you … Ask him: Is there another family member? When does the baby need food and drink?”

A lorry driver waiting at the traffic lights by the shop in a truck piled high with scaffolding, shouts: “Let him off!” before driving away, laughing.

In total, 13 people working in the five shops are arrested on suspicion of modern slavery and human trafficking offences, and another seven are arrested on suspicion of immigration offences and possessing counterfeit goods, mostly counterfeit cigarettes. Five children and nine adults are deemed to be vulnerable and taken to a temporary reception centre. The council says later that no one was taken into care, because “police weren’t able to establish that any of the young people were children”, although 10 children were found working in Southwark’s nail bars earlier in the year and placed with foster carers. It is unclear what happened to the baby.

Mark Rogers, the detective chief inspector leading the operation for the Metropolitan police’s central specialist crime unit, says he is happy with how things have gone. “Human trafficking, modern slavery and sexual exploitation often occur in plain sight, and it is often the case those carrying out these offences exploit those from less fortunate backgrounds who have travelled to our country for a better life, in the knowledge these individuals will carry out hard, labour-intensive work to provide for themselves.”

So, how can customers tell if a nail bar is not all it seems? Kevin Hyland recommends looking out for anything that doesn’t look right. “The price is sometimes an indicator but there are other signs.” Are the instructions given through a third party? Are you told: sit here, and that person will do your nails? There should be some ability to interact with the staff; does the worker carry on in silence, never removing the protective face mask? Is there a man sitting at the door, behaving in a dominant way?

Yet, ultimately, it shouldn’t be up to the customer to navigate this uncertainty, he argues, and councils should be doing more to inspect and shut down dubious salons. Southwark council has been more proactive than most, but points out that with a 50% cut in government funding over the past decade, protecting the work of trading standards teams is challenging.

Samantha Sweet, who runs Creative Nail Design, says it is impossible to tell which discount salons are likely to be exploitative. “If we knew more about the discount places I think we would choose different places. Some of them are absolutely fine and employ people legally. But I don’t think the general public think about it; they think – well it’s dead cheap and dead quick.” As a benchmark she said the average gel polish treatment should cost at least £25. But, she says “part of the problem is that in the cheaper salons, people don’t talk anyway – they hold out one hand and they’re on their mobile on the other, and then they swap hands.”

Millie Kendall, CEO of the British Beauty Council, says two decades ago she only knew of two nail salons in London, but new products, (extensions, fillers, shellac) and the rise of instagram sharing of nail art has made this a rapidly accelerating industry with multiple shops on most high streets. “The business has changed beyond recognition. Nail art has changed the game and made it a more creative industry. The flip side is that we are very under regulated and that’s a real problem for us. Bad products are being used, people get funguses, skin problems and there are slaves.” She hopes the government will move to license the industry.

Mark Rogers says he hopes media coverage of the arrests will “continue to raise the public’s awareness of these shocking crimes.” But even when people learn about the issue they tend not to believe it could affect the salon they use; it is hard to understand that you could be in such close proximity to someone who has been trafficked, holding your hand, and silently painting bright varnish on your nails.

Despite Southwark’s high-profile campaigns, online reviews of other nail bars in the borough continue to reveal how clients’ irritation with the language barrier is carefully weighed up against the joy of a cheap pedicure. Despite the intimacy involved in the treatment, hands and feet being washed and tended to by strangers, many seem remarkably uncurious about the workers, and concern for their welfare seems negligible. One customer writes: “The staff were rude both in person and on the phone, some barely spoke any English, you could clearly see they didn’t want to be doing the job. Got a manicure and pedicure – the job was just about mediocre.”