Waiting nervously to be tested for HIV and other diseases was the last thing Mike - not his real name - expected to be doing at nine o'clock on a hot Monday morning in July.

The undercover police officer had been bitten on the upper arm by Gilbert Muasa, a 23-year-old Kenyan drug dealer who had resisted arrest after being caught selling cocaine late at night on Hollywood Road, in Central.

As a matter of precaution, Mike underwent a blood test.

Muasa bit a second undercover officer before being handcuffed and bundled into an unmarked police van. The African has been in Hong Kong since last year, seeking asylum on the grounds that he faces torture in his home nation. On September 8, Eastern Court jailed him for 12 months for supplying dangerous drugs, four weeks for each bite and two weeks for obstructing the police, to be served consecutively.

The Kenyan turned to the drug trade after struggling to survive on official handouts, he says; asylum seekers in Hong Kong cannot legally work in the territory.

A year ago, the drug trade in Central's Lan Kwai Fong and SoHo became so blatant that anyone walking along Wyndham or D'Aguilar streets at night would probably have had to run the gauntlet of several dealers.

The hub of this drug activity is at the elbow of D'Aguilar Street, opposite Stormies bar, where a 7-Eleven opened at the beginning of last year. The relatively small district of LKF is now home to six of these convenience stores, dubbed Club 7/11 by some patrons, selling cheap booze and encouraging more revellers to drink on the street.

Into this nightly maelstrom has strolled a new wave of drug dealers. The majority of these opportunists are Gambian, or claim to be, and a few are South Asians. They tend to offer expatriates cocaine or marijuana.

Their presence in the area is shocking for its blatancy; the dealers congregate in small groups, away from the bars, and don't appear to be partying. They tend to have a mobile phone, rather than a drink, in their hand.

Assistant district commander for Central, Mark Ford McNicol, explains that the mostly African dealers began to congregate in Lan Kwai Fong, SoHo and Wan Chai about two years ago, but the problem escalated at the end of last year, when from September police efforts were focused on Occupy Central. They took their eye off Lan Kwai Fong.

The Central Special Duty Squad, headed by local undercover inspector " Rick", launched its drugs crackdown in January.

"The teams responded quickly, dealing with the drug gangs who were operating blatantly," says Ford McNicol.

Because of the gangs' international clients in Lan Kwai Fong, it made sense to deploy undercover expatriate officers as well as local decoys.

"It's been very successful, especially with the focus and commitment of one particular undercover officer."

To date, 64 drug arrests have been made, with 50 convictions: 35 for dealing drugs and 15 for possession, with total jail time awarded hitting 37 years. Seventy per cent of the 64 arrested were African, 35 of those Gambian. Of the total, 49 were asylum seekers. Rick's unit is due to receive a team commendation and Mike an individual commendation, in his case for arresting 20 dealers, who have been sentenced to a total of 27 years' jail time.

So what's fuelling the boom of the drug trade in Lan Kwai Fong?

In short, the amped-up street-carnival atmosphere, the shifts in visa policies in Hong Kong and Taiwan for Gambians, and the ready supply of drunken wealthy expatriates who fail to realise the abysmal quality of the drugs supplied have provided a ripe market. Police laboratory analysis shows the biggest component of Lan Kwai Fong street cocaine is often paracetamol.

"If buyers knew this they might be less keen to shell out HK$1,000 to HK$1,500 per gram. It's seriously cut: 0.2 of a gram is cocaine, if you're lucky," says Ford McNicol, adding that those taking such drugs are risking their lives.

Police efforts, he stresses, are not just focused on the street dealers, but also on catching the big fish supplying the drug trade.

IT'S GONE MIDNIGHT. Central Vice Squad's undercover team, headed by Rick, are dotted around the Lan Kwai Fong area in plain clothes.

"Wear trainers, you'll be slipping on vomit," Mike advises.

Stationed between Stormies and the 7-Eleven, photographer Dean Cox and I try to blend in with the crowd; something we became accomplished at, in the three months from September, during which we observed the police operation on six weekends.

Five young, casually dressed African-looking men are hanging around the steps to the alley behind 7-Eleven, which doubles as a urinal at night. The street is heaving. One at a time, Western men approach the Africans. Whispered conversations result in nods, hasty texting, then the suspected dealer disappears, presumably to access his drug stash. The customer waits nervously until the man returns minutes later. The dealer and the customer disappear briefly into the alley, the sale is made and the African resumes his patch.

Soon after, one of the dealers in this group is caught selling to Mike; Rick's undercover officers swoop in, handcuff the suspect and march him to the nearby waiting unmarked van.

Tonight, the suspect is a 30-year-old Gambian torture claimant named Lamin. Unlike Muasa he goes quietly, as if he knows the routine. And indeed he does - Lamin was released from prison the day before after serving eight months for possession of cocaine, and it was Mike who caught him on that occasion, too. This time around, Lamin will be sentenced to 16 months for dealing cocaine when the case goes to court.

"Some of these guys are not very smart," observes Rick.

On one night in May, Rick's team arrested five Gambian dealers. But the dealers have learned how to evade the police.

They have also become wary of us. Dean and I have explained we are journalists, not police, but with us having photographed several arrests they are suspicious. A group we've nicknamed the "gang of three" is becoming increasingly hostile. But on nights when they look potentially amenable, we strike up conversations and try to discover their story. "Agent Orange", as we've dubbed the man with short dreadlocks who regularly wears an orange football shirt, says he's called John, and claims to be Ghanaian one week, Gambian the next.

Things stay calm until one October night when he and a friend are searched by police, a regular occurrence. No drugs are found but after the men spot us taking photos, tempers flare.

Agent Orange, aka John, rounds on us angrily, gesticulating and shouting that the police are racist.

"Why do they just search us, not Chinese, not Europeans? It's because our skin is black," he yells.

Fearing we are in danger, undercover police descend.

We retreat to Al's Diner where the manager, Hartwig Harvey, tells us African drug dealers have become a constant headache for Lan Kwai Fong bar owners, hassling and discouraging customers.

As the weeks pass, the game gets tougher for both the cats and mice. The dealers get cannier and catching them becomes harder. After each arrest, those who manage to slip away hastily circulate photos of the undercover police decoy.

Some start to display defiance. On one occasion, one of them blows marijuana smoke in my face.

But Rick has an ace up his sleeve. One Saturday night, something changes among the group of suspected dealers, and they start rejecting all but regular customers. There is an atmosphere of alarm. The group appears to be constantly texting, and much darting about ensues.

Later Rick explains his team had seized a HK$10,000 cocaine stash hidden nearby.

"No arrests tonight but we've ruined their weekend," he says dryly.

HONG KONG HAS BECOME a magnet for Gambians over the past two years. Due to historic Commonwealth links - the Gambia is also a former British colony - Gambians were granted an automatic 90-day stay in Hong Kong on arrival, until the Immigration Department changed the rules in February, making it necessary for them to have a visa before entering the city.

When their period of stay expires, most Gambians make asylum seeker or "non-refoulement" claims, enabling them to remain while their applications are considered. They are not permitted to work, but they receive monthly rent and food vouchers worth HK$3,000 and a monthly cash travel allowance of HK$200 to HK$400. According to the Immigration Department, the applications of "non-refoulement" claimants, or "Form 8" holders, as the police call asylum seekers (Form 8 being the temporary ID document they receive), are usually processed within 25 weeks. New targets are aimed at shortening the procedure to 15 weeks.

In practice, however, "processing can take up to a year by the time they go through the first level, and then there is the appeal," says human rights lawyer Mark Daly. "But there have been repeated failures to speed up the system and I have known people be here for 15 years."

Few claims succeed.

There were 10,628 non-refoulement claimants at the end of last month in Hong Kong, up from 10,450 at the end of September. Of the 10,628, 167 were Gambians, representing the largest group of African claimants by nationality.

There are, however, no truly successful "asylum seekers" in Hong Kong, because the territory is not a signatory to the relevant United Nations convention. But it does have a legal obligation to not send back would-be refugees who face torture or degrading treatment in their home country, under the UN Convention against Torture.

Therefore, regardless of the outcome of their non-refoulement claim, asylum seekers cannot settle in Hong Kong and will eventually be deported when the alleged risk they face has subsided or is found to be unsubstantiated.

So why come to Hong Kong if the SAR does not shelter asylum seekers in the long term?

In Lan Kwai Fong, early on a Monday night, a friendly asylum seeker called Michael says he came to Hong Kong from the Gambia because his friends told him it was a good place to get a job. But the 22-year-old is finding it expensive, cannot work and has to ask his mother to wire him money.

Does he face persecution at home? He shakes his head, adding he will return home soon.

Another Gambian, Shannon, says he is 27 and also a Form 8 torture claimant. Asked what torture he is fleeing, he smiles: "I have some family problems."

The Gambia is a tiny West African river state with a population of 1.8 million. According to a recent Human Rights Watch report on the country, titled "State of fear: arbitrary arrests, torture and killings", since seizing power in 1994, President Yahya Jammeh has ruled with "often ruthless repression", silencing dissent and independent media, and using state security forces to intimidate and gag those who disagree with his government. "The population lives in a climate of fear, in which government justice and accountability for abuses is utterly beyond reach," the report said.

The next stop in our search for answers is Chungking Mansions, in Tsim Sha Tsui, and sweet masala tea with an asylum seeker who has been in Hong Kong for five years.

He speaks under the condition of anonymity; asylum seekers are often reluctant to be identified as doing so could put their families back home in danger.

Gambians, he explains, have traditionally not come to Hong Kong as traders, nor as tourists. But when Jammeh abruptly broke diplomatic ties with Taiwan in November 2013, Taipei stopped extending visas to Gambians. Hong Kong being the nearest Commonwealth-friendly visa-free territory, Taiwan's sizeable Gambian community headed here, becoming torture claimants when their visas ran out.

"[In the Gambia] the population lives in a climate of fear, in which government justice and accountability for abuses is utterly beyond reach."

Realising they couldn't work, many became drug distributors, he explains.

"But there were also Gambians coming straight from the Gambia, so we didn't know who was who, who was seeking political asylum and who was an economic migrant."

Some Gambians arrive at the airport and go straight to Kam Tin and Yuen Long, in the New Territories, he adds. They join relatives there, working in the second hand car and container trades, earning HK$3,000 to HK$4,000 a month.

"But lots get caught working illegally and spend one-and-a-half to two years in prison," he says, "So the smart ones go to the club areas at night and have someone supplying them with drugs to distribute.

"If you can earn HK$3,000 to HK$4,000 working illegally in Kam Tin and get two years in jail if you get caught, or you can work illegally selling drugs and get two to three months for possession of one or two grams [dealers get longer] and earn much more, of course, you will choose drugs. Then after two or three months [in jail] you can start again and make more money."

A street dealer will typically make HK$200 to HK$300 for each gram of heavily cut cocaine sold.

In Yuen Long, no illegally employed Gambians will talk but, sitting under the concrete stilts of a huge flyover, a well-educated Gambian former civil servant tells his story.

Strongly associated with the former Gambian political regime, Jim, not his real name, decided to leave his home country last year.

"Believe me, I did not leave a good job and my family to starve in Hong Kong without good reason," he says.

He last saw his best friend in 2006, when the journalist was taken away by government security forces and tortured. He is sure his friend did not survive. "You can be tortured for nothing, anything and few people survive that." 

Jim, 35, enrolled to study political science at a university in Guangdong province. On arrival, however, they wanted him to study Chinese for a year first.

"You have to survive by any means. For most that means working illegally."

A friend advised him to go to Hong Kong, saying, incorrectly, that he could be an asylum seeker here.

"I had wrong information," he admits. Now after a year, his torture claim application is making little progress, and he cannot afford the university fees in Hong Kong. "I'm just wasting time, going nowhere."

Unable to work, he is struggling. "You have to survive by any means. For most that means working illegally."

But the alternative does not bear thinking about.

"Gambia is not as poor as other African countries. It's not difficult to get money, of course there is unemployment but if you get a qualification, you get a job," he says. "The problem is the system of government. People are scared, they live in fear, in terror, that's why they leave.

"But here you can't trust other Gambians in case they are a security officer from home [sent to find those who have fled]."

He also believes many Ghanaians and Nigerians in Hong Kong are using fake Gambian passports, because they are easier to travel on. "I have met several 'Gambians' in Hong Kong who cannot speak our local language."

The Hong Kong police cannot tell the difference, he says.

"Nigerians and Tanzanians are the ones using these young guys," he says, repeating a theory that some but not all police Post Magazine spoke with supported: that Nigerians are luring the Gambians into the drug trade.

"The Gambians don't have the financial muscle to leave, so they become the prey. Some of them will tell you they got caught the first or second time they did it."

Jim can't abandon his torture claim and leave Hong Kong. If he gives up his claim, his status immediately reverts to "overstayer" - because torture claims can only be lodged when the initial visa has expired - and he will face several months in a Hong Kong jail.

When asked about this rule, an Immigration Department spokesman says: "That's the law." Is that not senseless? "No, it's the law."

The manager of charity Christian Action's Centre for Refugees, Justin Murgai, says, "These cases are certainly not representative of asylum seekers in Hong Kong, where we have thousands of people from the Middle East, Africa and other parts of the world who are genuinely seeking protection from war and persecution in their home countries … The attention such cases have received of late is tainting the way people view refugees and [diverting attention] from some of the real issues being faced by the community, from destitution and homelessness to years of delays in being screened and granted protection."

For many of Hong Kong's 10,000-plus asylum seekers it may yet prove to be Hotel California, where "you can check out any time, but you can never leave".