The UK’s first-ever Independent Anti-Slavery Commissioner has resigned while citing government interference in his role.

Kevin Hyland OBE said he stepped down “with a heavy heart” after four years in the position to take up a new post at a charity.

In a letter to Theresa May he praised her “personal leadership” in the fight against modern slavery, including the creation of his role, but said independence was “vital” for its success.

“At times independence has felt somewhat discretionary from the Home Office, rather than legally bestowed,” Mr Hyland wrote.

“I hope that any future incumbent can be assured the independence I am sure you intended as the author of the legislation.”

His resignation came weeks after a parliamentary committee found that modern slavery was not fully understood by the government, suggesting ministers had no idea whether the crackdown was working.

The prime minister did not directly address Mr Hyland's criticism in her formal reply, in which she praised the outgoing commissioner for “shining a spotlight on the scale and nature of modern slavery and internationally”.

Mr Hyland thanked Ms May for her personal support and said he would be happy to assist the government on modern slavery in the future.

Police warn modern slaves 'staffing nail bars across UK' as Vietnamese gang jailed in landmark case

He is to become chief executive of ChildFund Ireland and there has been no timescale set for the appointment of a replacement by Downing Street and the Home Office.

Mr Hyland took up his post a year before the Modern Slavery Act 2015 into force and the original three-year term was extended in November.

The law guarantees the independence of the Independent Anti-slavery Commissioner, who is responsible for improving the prevention, detection, investigation and prosecution of slavery and human trafficking offences.

Mr Hyland said the number of potential victims referred for support in Britain had doubled in the past three years, while crimes recorded are up 500 per cent and dedicated operations by police and other agencies are on the rise.

In his resignation letter, he praised a campaign orchestrated by The Independent and Evening Standard last year as well as work to improve commercial supply chains and international cooperation.

Mr Hyland said: “Much work remains, but I depart knowing that awareness at both the highest level and at that critical working level has never been greater.

“As the inaugural incumbent in a unique role there have predictably been some learning points for all around the precise nature of the independence set by the founding legislation, but I leave the role confident that my successor can only benefit from this learning.”

The Focus on Labour Exploitation (Flex) group accused the Home Office of hampering progress with its “tight control” over Britain’s modern slavery response.

Campaigners said the National Referral Mechanism should not have been brought in-house last year amid “hostile environment” immigration policies that are seeing potential victims arrested.

In decisions on non-EU nationals only, the Home Office recognised 14 per cent of referrals as victims of trafficking, but the National Crime Agency’s dedicated unit recognised 67 per cent.

Modern Slavery in the UK Show all 13 1 /13 Modern Slavery in the UK Modern Slavery in the UK NCA has launched a touring photographic exhibition which aims to portray the signs of slavery and exploitation. Entitled ‘Invisible People’, the exhibition will tour the country as part of the National Crime Agency’s campaign to raise awareness of modern slavery and human trafficking. National Crime Agency Modern Slavery in the UK Child trafficking Child trafficking for sexual exploitation Traffickers use grooming techniques to gain the trust of a child, family or community. The children are recruited, transported and then sold for sex, often returning to their homes immediately afterwards, only to be picked up by the same people again. This is happening here in the UK, to migrant and British-born children. Spot the signs of child trafficking: Often, children won’t be sure which country, city or town they’re in. They may be orphaned or living apart from their family, in unregulated private foster care, or in substandard accommodation. They may possess unaccounted-for money or goods or repeatedly have new, unexplained injuries. National Crime Agency Modern Slavery in the UK Agriculture Some workers in the farming sector, harvesting grains or root vegetables, tending livestock or fruit picking, are being exploited every day in the UK. Victims of this crime in the agricultural sector are often Eastern European men and women, who were promised a job by traffickers, or they could be individuals on the fringes of society, homeless or destitute. Through threats, violence, coercion or forced drug and alcohol dependency, they’re enslaved, working for little or no money, living in squalid conditions having had their identity documents taken from them. Spot the signs of exploitative labour in agriculture: Agricultural slaves often have their wages paid into the same bank account, meaning an illegal gangmaster is likely collecting all their wages. Exploited agriculture workers often don’t have suitable protective equipment, working instead in cheap sports clothing and trainers, and don’t have a different change of clothes from day-to-day. National Crime Agency Modern Slavery in the UK Food processing Polish or Slovakian men are brought to the UK with the offer of employment and, after arrival, gangmasters seize documents, opening multiple bank and utility accounts in their names – but refuse to handover access to the accounts or bank cards. Hours are long and the work is gruelling and dangerous. Workers are abused and are controlled by threats of harm to their families at home. Spot the signs: Those exploited wear inappropriate clothes and often no safety gear – despite working with dangerous and life-threatening equipment. They may often have untreated injuries and be refused medical attention, and will live and work in agricultural outhouses. National Crime Agency Modern Slavery in the UK Construction Labour-intensive sectors like construction, where temporary and irregular work are common, are high-risk sectors for forced labour. With new homes, offices and buildings being constructed or upgraded in great quantity, labour exploitation is the second most common type of modern slavery, after sexual exploitation. Spot the signs of exploitative labour in construction: Exploited workers are often not provided with protective clothing or equipment, and may show signs of abuse or carry old untreated injuries. Slave workers are also likely to work extremely long work hours for six or seven days a week without any leave. Photographer Rory Carnegie, said: “I wanted this image to communicate that despite being forced to live, eat, wash and sleep – where they’re working, in cramped and unhygienic conditions, that there is a human instinct to domesticate. I wanted to show how there is still hope and dignity in the most squalid and difficult of circumstances.” National Crime Agency Modern Slavery in the UK Maritime In the tough maritime industry young men, often Filipino or Indian, Eastern European or African, are promised a better life, but instead find themselves in a cycle of debt and exploitation. Unable to read, they are offered a job, given papers to sign and begin working on a trial-basis, only to be told they have failed and owe money, and have to work more to settle the debt. They may be forced to work for long hours in intense, hazardous and difficult conditions. Photographer Rory Carnegie, said: “In the 80s, Chris Killip published a series of images called In Flagrante, and these images were at the forefront of my mind while composing this shot. I wanted to show the utter desperation of these men - how passed their limit they are. The broken floats and the entire decaying environment around him, I saw as a metaphor for his existence.” Rory Carnegie/National Crime Agency Modern Slavery in the UK Forced prostitution Each year, women from across Eastern Europe and West Africa are lured to the UK by the dream of a better life. Whether by fake migration services or unscrupulous individuals who befriend and then betray them, women fall into a dark spiral of sexual exploitation and forced, unpaid prostitution, unable to escape. Photographer Rory Carnegie, said: “What I really wanted for this image, was to depict how women are used as commodities, the complete control slavery has over them – the helplessness of having to sit and wait for man after man, until no more men arrive. I wanted the image to show how lonely and eventually numbing that experience is, and for that ugliness to be contrasted against the bright blue of the wig – a fancy dress item that we would usually associate with a fun event – but here is used as a disguise, perhaps of her own identity to herself - to further emphasise how unjust the situation is.” NCA Modern Slavery in the UK Cannabis farming The cannabis industry hides a dark secret in the house next door. Gangs bring young boys to the UK from countries like Vietnam and deliver them to a house where, once in, they won’t be able to leave. Forced to tend cannabis plants that fill specially rigged houses, the boys are often locked in and forced to work, sleep and eat in one confined and dirty room. The chemicals used on the cannabis are poisonous, and often victims don’t know where they are or how to get help if they do escape. The eyes, ears and compassion of the local community are essential. Spot the signs: Aside from the strong and prolonged smell of cannabis, have you noticed a house that looks unusual? Are the windows covered or usual entry points blocked? Buildings might be over-heated – in very cold weather is the roof without frost, because the house is being kept warm to grow plants National Crime Agency Modern Slavery in the UK Agriculture Some workers in the farming sector, harvesting grains or root vegetables, tending livestock or fruit picking, are being exploited every day in the UK. Victims of this crime in the agricultural sector are often Eastern European men and women, who were promised a job by traffickers, or they could be individuals on the fringes of society, homeless or destitute. Through threats, violence, coercion or forced drug and alcohol dependency, they’re enslaved, working for little or no money, living in squalid conditions having had their identity documents taken from them. Spot the signs of exploitative labour in agriculture: Agricultural slaves often have their wages paid into the same bank account, meaning an illegal gangmaster is likely collecting all their wages. Exploited agriculture workers often don’t have suitable protective equipment, working instead in cheap sports clothing and trainers, and don’t have a different change of clothes from day-to-day National Crime Agency Modern Slavery in the UK Forced prostitution Spot the signs of forced prostitution: Victims of this type of crime might appear withdrawn or scared, avoid eye contact, and be untrusting. Poor English language skills could indicate exploitation because it suggests someone else must be arranging the work. A brothel is likely to be an average house on a normal looking street, but may have curtains which are usually closed and many different men coming and going frequently. National Crime Agency Modern Slavery in the UK Maritime Spot the signs of exploitative labour in the maritime sector: Victims might appear withdrawn or frightened, often unable to answer questions directed at them or speak for themselves,. They might be afraid of authorities like police, immigration or the tax office, and may perceive themselves to be in debt to someone else. They may not have been given proper protective equipment so can suffer illness or injury. Photographer Rory Carnegie, said: “Throughout the series of images, I wanted to juxtapose the harshness of the lives of slaves against bright primary colours – colours we traditionally associate with happiness or a feeling of wellbeing – to provoke a reaction. The image, as rich as it is, communicates how completely uncomfortable this person is. I wanted to show how his body is not his own, and how he has no right to avoid hardship, avoid the ice, or wear better shoes, he is utterly controlled.” Rory Carnegie/National Crime Agency Modern Slavery in the UK Food processing Photographer Rory Carnegie, said: “This image communicates utter exhaustion and dejection. We can see how dire his situation is. He has no protective gear on, and we can see the extreme tiredness that leads him to a place of anxiety and distraction, where he doesn’t care about whether he’s operating machinery safely, or putting himself at risk.” National Crime Agency Modern Slavery in the UK The exhibition comprises a series of large, freestanding cubes displaying images capturing snapshots of life within different types of modern slavery - in agriculture, construction, maritime, cannabis farming and food processing, child trafficking for sexual exploitation and forced prostitution. Each image comes with written commentary describing what the viewer is seeing, and information about signs which may indicate someone is a victim. National Crime Agency

Caroline Robinson, director of Flex, said: “When potential slavery victims are arrested during immigration raids then it plays into the hands of trafficking gangs, who use fear of the authorities as a way to control people. It also prevents people coming forward to report their exploitation.

"Without strong independent oversight of the modern slavery response, and a clear separation with immigration control policies, then many of the Prime Minister’s strong commitments to tackle modern slavery will be undermined and we will see more of society’s most vulnerable arrested instead of receiving the help they desperately need.”

Efforts to combat modern slavery have spread into fields including nursing, business and public awareness campaigns to help people spot the signs of sexual and labour exploitation.

More than 600 live police operations are currently underway and in 2017, over 5,000 potential victims of modern slavery were offered help under the UK’s National Referral Mechanism.

A National Crime Agency report released in March revealed that British citizens had become the largest national group for the first time following a shift in the way police treat teenagers exploited to run drugs for “county lines” gangs.

Other common countries of origin include Albania, Vietnam, China, Nigeria, Romania, Sudan, Eritrea, India, Poland and Pakistan, but 116 different nationalities are known to be affected.

The majority of modern slaves identified are subject to forced labour, sexual exploitation or domestic servitude.

Victims have been found in a range of legal and illegal trades in the UK, including nail bars, cannabis farming, prostitution, flower-picking and at hand car washes.

Victoria Atkins, the minister for crime, safeguarding and vulnerability, described the UK’s response as “world-leading”.

“Kevin Hyland has played a pivotal role,” she added. “He leaves a strong legacy, and the Home Office is working with the Commissioner in his final months to see how this important role can be further strengthened.