Every year thousands of women are trafficked to European cities and put to work having sex with men. Jewel, a young Nigerian who had expected to become a carer, eventually managed to escape thanks to two chance meetings.

"I just saw light. It's very often dark where I come from because there's no electricity… But everything here was just blinking - it was very beautiful."

Jewel - not her real name - is describing her arrival in Denmark.

"I was thanking God for the opportunity to be in this country. I was looking forward to starting work."

Jewel caught a flight from Nigeria thinking she was going to work with old people.

"People who get trafficked go through Libya and usually take buses and boats. But this was so well organised that it wasn't suspicious at all," she says.

The International Organisation for Migration has estimated 80% of Nigerian women travelling overland, then attempting to cross the Mediterranean, are trafficked into the European sex trade. Jewel knew of women who had suffered that fate after making the perilous journey, so when her trip began at Lagos airport, she was reassured.

In Copenhagen, she was met by a Nigerian woman, who took her the following day to Vesterbro, Copenhagen's red light district.

"I was looking around for some sort of hospital," Jewel remembers.

They walked the streets for a while, Jewel being told to take note of her surroundings.

Then the woman dropped a bombshell.

"She said, 'This is where you're going to be working.' I looked round to see if she was pointing at a building I hadn't noticed. But no - she meant where we'd been walking. That's when she told me I was going to be a prostitute, and this was where I'd be hunting for customers. Then the whole of Denmark just crashed down on me…"

Jewel had one fortuitous meeting that night that would later be important - Michelle Mildwater from HopeNow, an NGO supporting trafficked people in Denmark, spotted the tiny, timid, 20-something woman and gave her a card with a contact number on it.

Jewel's Nigerian boss - her "madam" - told her not to trust this English woman with a bike. Then she quickly found Jewel her first customer.

"The man gave her 4,000 kroner (£450 / $620) to take me home, and then my madam just walked away," says Jewel.

"He drove me for what seemed like forever. I didn't speak the language at the time and I had no idea what he was saying - we had to use Google Translate to communicate. It was scary."

In the months that followed, selling sex did not become any easier for Jewel.

"I wasn't good at it. I was that shy one in the corner. But I always got found because the regulars know when a new person arrives, and they wanted a piece of the new person."

In the most recent figures released by the EU, more than 14,000 trafficking victims were registered in 2017/2018 - but this will be the tip of the iceberg, because they represent only identified cases. Half were from outside the EU, with Nigeria one of the top five nationalities.

Sexual exploitation continues to be the main purpose of trafficking, according to the European Commission, and in a single year the criminal revenues derived from it are estimated at a staggering 14bn euros (£12bn / $16bn).

The women who earn this money are told they owe their traffickers huge sums for travel and accommodation.

"They are debt-bonded," says Sine Plambech, a senior researcher in the Department of Migration at the Danish Institute for International Studies.

"Nigerians are one of the migrant sex worker groups with the highest debt. It could be between 10,000 and 60,000 euros. And when you have that kind of debt, you need to make a lot of money fast. And if you don't have papers that allow you to work, the fastest way to earn money is in the sex industry."

Jewel's traffickers said she would have to pay them 42,000 euros, in regular instalments. To underline their point they summoned her to a frightening meeting in a cemetery, the day before she flew out of Nigeria.

"I was forced to take an oath that I was going to pay the money no matter what, and that I was not going to reveal who trafficked me. If I did, so many bad things were going to happen to me and my family."

Once Jewel was in Denmark, the traffickers menaced her family in Nigeria.

"People just came into the house and they wanted my grandmother to talk to me about not having any ideas about reporting them to the police, or not paying the money. So every time I called her, she was always crying on the phone and reminding me that I had made this deal with these people - I had to pay or something would happen to them."

Jewel was under immense pressure so did not feel she could be discriminating about the clients she serviced inside and between parked cars on the streets of Vesterbro, or in their homes.

"You cannot say no. You have to say yes, because there are 10 or 15 other women looking at that same guy wanting to make some money that night," she says.

But going with a customer to his home could be enormously risky.

"I could have died that night I was forced to remain in the bathtub," she remembers, still traumatised.

"The man I had to go home with asked me to get in the bathtub. And I thought, 'OK - he wants me to clean up or something.' Then he went out and came back with two buckets of ice. And he started pouring this ice on me in the bath. And I was in there naked and it's in the middle of winter…"