Britain must ensure human traffickers do not exploit uncertainty surrounding Brexit, from its future migration policy to cooperation with European law enforcement agencies, the nation's anti-slavery commissioner said on Friday.
Sara Thornton said Britain would need to arrange new partnerships across Europe to bring traffickers to justice and "stress test" migration systems to protect workers from labour abuse as the country's departure from the European Union looms.
While the exact nature and date of Brexit is still unclear, activists and police say Europe-wide anti-trafficking efforts could be hampered and that migrant workers risk being exploited under government plans to minimise labour shortages.
"Protecting victims and prosecuting traffickers is not enough," Thornton said in a statement. "To stop modern slavery from happening in the first place, we need to do much more to tackle the systems and structures that allow it to thrive."
"Those who traffick and trade in human beings will take any opportunity for exploitation," said the former police chief, who took up the post in May after the inaugural commissioner quit mid-2018. "We must not let them threaten our joint security."
Thornton on Friday published her strategy to tackle the crime in the coming years, and said her priorities included securing more prosecutions and improving support for victims.
Too many suspected modern slaves are living in limbo as they wait to learn if they will be recognised as victims and granted more support, she told the Thomson Reuters Foundation in August.
About 7,000 possible slavery victims were found in Britain last year - up a third on 2017 - while there are an estimated 136,000 modern slaves across the country, according to the Global Slavery Index by human rights group Walk Free Foundation.
Thornton also urged businesses, public services and the government to "do all that they can" to prevent trafficking and slavery from taking place in their operations and supply chains.
Britain has positioned itself as a leader in the global drive to end slavery since passing the 2015 Modern Slavery Act to jail traffickers for life, better protect vulnerable people, and compel big companies to outline their anti-slavery measures.
Yet a government-ordered review of the world-first law this year found that a lack of convictions, limited awareness among and training of professionals, and problems around data collection have blunted Britain's anti-slavery response.
In a report published on Thursday, the Home Office (interior ministry) said it was committed to reforming its support system for victims and ensuring that children received specialist care.
There are more than 1,400 active law enforcement investigations involving modern slavery across Britain, up from about 200 at the end of 2016, according to government data.
"We have made it harder than ever for trafficking gangs to evade justice," said Britain's interior minister Priti Patel.
The Crown Prosecution Service secured 191 modern slavery convictions last year - up from 180 in 2017 - but the conviction rate dipped to 65% from 68%, the statistics showed.
The chief executive of charity Focus on Labour Exploitation said she was concerned that the British government was "failing to grasp what meaningful protection should look like".
The government must introduce a joint liability law that would make companies legally liable for worker abuses that occur in their supply chains, and overturn policies that leave migrant workers at risk of exploitation, according to Lucila Granada.
"Without repealing ... hostile environment policies putting people at risk, migrant exploitation will continue to thrive." 
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