SiteKiln gives you plain-English information, not legal advice. If someone is in immediate danger, call 999. If you suspect modern slavery or labour exploitation, call the Modern Slavery Helpline on 08000 121 700 (free, 24/7, anonymous).
# I Think There's Labour Exploitation on My Site, What Do I Do?
You're not the police and you're not social services, but if something on site feels wrong, it probably is. Your job is to spot it, log it, and pass it to people who can actually intervene.
1. What modern slavery looks like on a construction site
On a normal site you'll always have a mix of workers, languages and subcontractors. Modern slavery is when people are controlled, not just badly treated.
Red flags on construction jobs:
- Workers who never speak for themselves · a "boss" or translator answers every question, even simple ones like "what's your name?"
- People who don't have their own passport or ID, or say "the boss keeps our documents"
- Groups being transported in and out together very early or very late, not mixing with anyone else, and never seen off site alone
- Workers living on site or in overcrowded accommodation, often all from the same country, in poor conditions
- Wages paid into one bank account controlled by someone else, or workers saying they "don't know" what they earn
- People looking constantly tired, hungry, scared, or jumpy · watching whoever seems to be in charge before they answer anything
- Workers who can't leave when they want, talk about "debts" or "fees" for getting the job, or say they owe the gangmaster money
- No PPE, no CSCS cards, no induction records · because the exploiter doesn't care about compliance
- Workers wearing the same clothes every day, with no personal belongings on site
Construction is consistently in the top three sectors for reported forced labour in the UK, alongside car washes and agriculture.
2. How big is this problem?
The UK has a formal system called the National Referral Mechanism (NRM) for identifying potential victims of modern slavery.
- In 2024, 19,125 potential victims were referred to the NRM · a record high, up 13% on 2023
- In 2025, referrals jumped to 23,411 · a further 22% increase
- Around a third of all referrals are for labour exploitation, and construction is repeatedly flagged as one of the main sectors
- Most adult labour exploitation victims are male. Many are Eastern European, African or Asian nationals · but British workers can be exploited too
- The Gangmasters and Labour Abuse Authority (GLAA) has run multiple operations targeting construction sites specifically
"That doesn't happen here" is not true. It does, and it's being recorded in increasing numbers.
3. The law, what you need to know
You don't need to quote sections on site. But it helps to know where you stand.
The Modern Slavery Act 2015 makes forced labour, human trafficking, servitude and slavery criminal offences in England and Wales. Scotland has the Human Trafficking and Exploitation (Scotland) Act 2015. Northern Ireland has the Human Trafficking and Exploitation (Criminal Justice and Support for Victims) Act 2015.
Section 52 of the Modern Slavery Act 2015 places a duty to notify on specified public authorities, police, the NCA, local authorities, and certain other bodies. If they encounter a potential victim, they must notify the Home Office.
There is no legal duty on ordinary workers to report. But there is a strong moral and practical reason to, because these people often cannot ask for help themselves.
Your protection if you speak up: if you raise concerns with your employer or main contractor about potential criminal activity, that counts as a qualifying disclosure under the Employment Rights Act 1996, Part IVA (the whistleblowing legislation). This means:
- You should not be dismissed or subjected to any detriment because you reported it
- If you are, you may have a claim for automatic unfair dismissal or detriment
- Any contract clause that tries to prevent you from reporting criminal activity is legally void
- This protection covers workers and employees, not just permanent staff · so agency workers and CIS subcontractors can also be protected in many circumstances
The protection isn't perfect in practice, but it's there. Unions, ACAS, and specialist employment solicitors use it regularly.
4. Who to contact
You do not have to sort this yourself. Your job is to pass the concern to people who can.
Modern Slavery & Exploitation Helpline (run by Unseen)
08000 121 700 · free, 24/7, 365 days a year
modernslaveryhelpline.org, you can also report online
You can stay completely anonymous. They advise on what to do and can pass information to police and specialist agencies. This is the single best first call.
Gangmasters and Labour Abuse Authority (GLAA)
0800 432 0804 | gla.gov.uk
The GLAA investigates labour exploitation and unlicensed gangmasters in high-risk sectors including construction. They have enforcement powers including the ability to arrest and prosecute.
Police
- 999 if someone is in immediate danger
- 101 for non-emergency concerns · mention "modern slavery" or "trafficking" and the call will be directed to the right team
- Most police forces have a Modern Slavery Coordination Unit or equivalent
HSE
HSE covers health and safety, but they work with police and GLAA on joint operations where there are modern slavery concerns combined with unsafe working conditions. If what you're seeing involves both exploitation and safety failures, you can report to HSE as well.
0300 003 1647 | hse.gov.uk
Your union
If you're in Unite, GMB, or another union, speak to your local rep. They can raise concerns with the employer or regulators and support you personally if there's backlash.
Your employer's whistleblowing channel
If your employer or main contractor has a modern slavery policy or anonymous reporting hotline (most Tier 1 contractors do), you can use it. But use it alongside the independent helpline or police if it feels serious, not instead of.
5. What happens when you report
If you call the Modern Slavery Helpline or GLAA:
- They'll ask what you've seen: how many people, what conditions, where, who seems to be in charge, vehicle registrations, company names
- They won't demand your name · you can give it or stay anonymous
- They risk-assess and pass information to the right agency (police, GLAA, local authority, NCA)
- You might not hear back, and you probably won't see a raid the next day. That doesn't mean nothing is happening · they often need to build a picture from multiple sources before acting
- Your call could be the one that tips the balance
If you report through your employer's internal channel:
- They should log it and escalate · internally and, where appropriate, to police or GLAA
- They are expected to treat your report confidentially
- They must not victimise you for raising it (whistleblowing protection applies)
- If they don't act, or if you suspect they're complicit, go directly to the Helpline or police
6. What NOT to do
Good intentions can make things worse if you're not careful.
Do not:
- Confront the suspected exploiter or gangmaster · these are criminals. You could put yourself and the workers at greater risk. GLAA and police repeatedly warn against direct confrontation
- Promise the workers you'll "get them out" · if you can't deliver, you may raise hopes and then leave them more vulnerable. Let specialists handle direct contact with potential victims
- Take close-up photos or videos of the workers' faces · this can identify them, put them in danger if the images are found, and may breach their privacy
- Post about it on social media with location details · you might alert the exploiter, who moves the workers before authorities can act
- Do nothing because you're "not sure" · you don't need to be certain. The official guidance is: spot the signs, share your concerns, and let trained professionals assess
What you CAN safely note:
- Site name and address
- Company names on vans, jackets, helmets
- Vehicle registrations
- Dates, times, rough headcount
- What you've observed: "workers seem to live in cabins", "always escorted", "no PPE", "one person holds all documents", "never seen alone"
That's the kind of detail the Helpline and GLAA find most useful.
7. If you're not sure but something feels wrong
You don't have to be 100% certain. Nobody expects you to be an expert on trafficking.
If you're on the fence:
- Write down what you've seen over a few days · times, behaviours, anything specific
- Call the Modern Slavery Helpline on 08000 121 700 and say: "I'm not sure, but here's what I'm seeing on this site"
- Let them tell you whether it sounds like modern slavery indicators. That's their job · not yours
- If they say it doesn't sound like exploitation, you've lost nothing. If it does, you might have given someone a chance to get out of a situation they can't escape on their own
You're not grassing for the sake of it. You're looking out for someone who has nobody else looking out for them.
What to do next
- If you're worried about someone right now, call 08000 121 700 (Modern Slavery Helpline) · you can be anonymous
- If someone is in immediate danger, call 999
- If you want to learn more about the signs, visit modernslaveryhelpline.org
- If you're a site manager or employer, check whether your business has a Modern Slavery Statement (required by law for businesses with turnover over £36m under s.54 of the Modern Slavery Act 2015)
Sources
- Modern Slavery Act 2015 · legislation.gov.uk/ukpga/2015/30
- Modern Slavery Act 2015, s.52 (duty to notify) · legislation.gov.uk/ukpga/2015/30/section/52
- Modern Slavery Act 2015, s.54 (transparency in supply chains) · legislation.gov.uk/ukpga/2015/30/section/54
- Human Trafficking and Exploitation (Scotland) Act 2015 · legislation.gov.uk/asp/2015/12
- Human Trafficking and Exploitation (Criminal Justice and Support for Victims) Act (Northern Ireland) 2015 · legislation.gov.uk/nia/2015/2
- Employment Rights Act 1996, Part IVA (whistleblowing) · legislation.gov.uk/ukpga/1996/18/part/IVA
- Home Office, National Referral Mechanism Statistics 2024 and 2025 · gov.uk/government/statistics/modern-slavery-national-referral-mechanism-and-duty-to-notify-statistics
- GLAA, Construction Sector Guidance · gla.gov.uk
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