Gwent Police has not brought a single charge under modern slavery legislation since its introduction in 2015, despite dozens of recorded cases.
The force launched a five-strong team of officers dedicated to combating human trafficking.
Despite a series of high profile raids on premises across the force area, no-one has been charged.
Modern slavery was introduced as a single, specific offence under the Modern Slavery Act, which came into effect in March 2015.
Since then, Gwent Police has recorded 46 instances, according to Home Office data up to the end of December last year.
Of the 23 cases that had been concluded by the time the data was released, none resulted in a suspect being charged.
Difficulty gathering evidence was cited as the reason for not bringing charges in 57% of cases – 30% where the victim didn’t support further action being taken, and 26% where they did.
Police closed the case without identifying a suspect in 43% of cases.
Examples of modern slavery include domestic servitude, forced sex work, or labour exploitation in industries such as agriculture, or in businesses like nail salons and car washes.
It can also involve criminal exploitation, such as children or vulnerable adults being recruited into the drugs trade.
Detective Inspector for Serious Organised Crime in Gwent, Andrew Tuck, explained that complex and lengthy investigations can take up to two years to complete and that a number of investigations are ongoing.
However, victims have been helped, even if those responsible for their misery have yet to be convicted.
DI Tuck said: “Within the area of ‘vulnerability’ and crimes concerned with it, traditionally, we have seen that it is very difficult to get a conviction as often victims are too scared to say they are being exploited or may not even realise they are being exploited.
“Since their inception in February 2018, The Modern Day Slavery Team in Gwent have been focused on increasing awareness of exploitation, in particular, ensuring officers and the public know what to do around the area of modern day slavery and human trafficking.
“As a result, we have seen a substantial increase in numbers of referrals. Through The National Referral Mechanism, we have seen our numbers increase from 29 victims in 2017 to 92 victims in 2018 in Gwent – these were all exploited people that have now been safeguarded by Gwent Police.
“Alongside this, Gwent Police were the first force in the Welsh region to identify a suspected human trafficker and consider them as a ‘Priority’ Individual, in much the same way organised crime groups are managed.
“We have trained over 1,500 people in awareness of modern day slavery – 18 staff in Gwent have attended a four-day Modern Slavery Specialist Investigator Course, and have intervened in circumstances of labour exploitation of vulnerable individuals.”
DI Tuck added that raids on premises such as car washes have improved “intelligence” on gang masters with the amount doubling in the last year.
A recent parliamentary report on modern slavery concluded that the practice “pervades every community” in the UK, and warned the number of victims could be in the tens or even hundreds of thousands.
Experts have warned that a lack of support for victims could be hindering investigations, after the rate of offenders being charged fell to a record low across England and Wales.
Police forces across the two countries have recorded over 10,000 slavery offences since 2015 – almost half of them in 2018 alone.
But just 3% of cases concluded in 2018 ended in charges being brought, compared to 19% in 2015.
The Human Trafficking Foundation said modern slavery cases were some of the most complex police may ever have to deal with, involving highly vulnerable and traumatised victims who may not want to help the police.
However, a spokeswoman said it was disappointing the increase in the number of victims being identified hadn’t led to a large increase in prosecutions or convictions.
“The lack of support and stability we provide victims is no doubt partly to blame for these low figures,” she said.
“Survivors of any serious crime would struggle to be able to trust authorities if they live in unstable accommodation with barely anything to live on, and do not know where they will be housed in a month or whether they will be made to return to a place that they know could lead to re-exploitation.”
She added that giving victims more incentives, such as the right to remain in the UK, would encourage more to help police “put their traffickers behind bars”.
The Home Office said the UK Government was committed to stamping out the “abhorrent” crime. A spokeswoman said: “Our world-leading Modern Slavery Act has led to thousands of victims being protected and hundreds of convictions.
“But we know there is more to do and are working with police to see what more can be done to improve their response to this terrible crime.”