The conviction rate for modern-day slavery offences in England and Wales over the last two years stands at just 1.9%, a Sky News investigation has learned.
Of the 17 police forces which held data on convictions, only 25 successful prosecutions were made between April 2015 and March 2017, according to a freedom of information (FOI) request.
That was despite a total of 1,265 slavery offences reported in those force areas.
Across all 38 police forces who responded to the FOI request, crimes recorded under the Modern Slavery Act rose by nearly 200% in two years.
Between March 2015 and April 2016 there were 788 offences - the following year 2,347 were recorded.
The Sky News investigation comes as a watchdog report claims police are failing the victims of slave drivers and human traffickers.
Cases are being shelved prematurely, investigations delayed by several months and clear signals of crimes missed, according to the assessment from HM Inspectorate of Constabulary and Fire and Rescue Services (HMICFRS).
HM Inspector of Constabulary Wendy Williams said: "Whilst modern-slavery cases can be complex and require significant manpower, many of the shortcomings in investigating these cases reflect deficiencies in basic policing practice.
"As a result, victims were being left unprotected, leaving perpetrators free to continue to exploit people as commodities."
While it was believed there were about 13,000 potential slavery victims in the UK, the figure is now thought to be in the "tens of thousands".
Gary Booth, UK programmes director for the charity Hope for Justice, described the current situation in the UK as "a human conveyor belt of slavery".
He says that recovering victims from traffickers only "hits them short term in the pocket" and unfortunately there are others overseas, in Europe, or the UK "who will be recruited" and quickly "fill that void".
"Law enforcement agencies are making inroads into disrupting these organised crime groups who just inflict human misery," he added.
Sky News has also learned that less than half of police forces in England and Wales have a dedicated anti-slavery unit.
Most of the forces who do have a unit introduced it within the last two years, since the Modern Slavery Act was introduced in 2015.
Hope for Justice has rescued nearly 600 victims of modern slavery to date, often working well with local police forces.
The numbers entering the government National Referral Mechanism (NRM), that sets slavery victims up in safe houses to protect them from their exploiters, is also increasing significantly year on year.
The National Crime Agency said that last year 4,273 people were referred through the mechanism, with more than 12,000 in total to date.
Nigel Oseman, a trainer for Hope for Justice, who works with frontline services to spot the signs of slavery, says "modern slavery and human trafficking is embedded here in the United Kingdom".
"It's amongst our communities," he said, "and it could well be in the streets that you live in and you won't even know about it."
There is one common factor amongst victims of slavery: vulnerability.
"If we got parked in the middle of a country where we couldn't speak the language," he says, "and we got spun around 10 times and all of our IDs taken off us.
"If someone then said 'go and survive' - whilst I don't consider myself vulnerable - I would become vulnerable very quickly.
"And if some of these victims have had an existing vulnerability then that just heightens things."
Filip, a victim of forced labour, told Sky News how he felt "like a bird that has escaped from a cage" following his rescue.
He said he had never heard of the term "modern slave" previously but described his time under the control of traffickers "as like a bit of hell".
"I can't take it to my head clearly," he said. "I was born a free man".