Construction Site Trespassing: What Are Your Legal Obligations If Someone Is Injured?

As one of the most at-risk premises for trespassing and illegal entry, construction sites are at a major risk of liability breaches. With the Occupier’s Liability Act 1984 bringing in stricter penalties for lapses in site security and potentially unlimited fines, illegal trespassing at construction projects is a huge concern.

What Does The Law Say About Construction Site Trespassing?

Under the Occupier’s Liability Act of 1984, property owners and occupiers have a “duty of care” to trespassers and uninvited visitors, even if they arrive while the property owner isn’t present. As per Section (3) of the Law, there are 3 specific stipulations which apportion liability to the property owner or occupier:

• They’re aware of the danger at the site or have a firm reason to believe that it may exist.
• They have a reasonable suspicion that trespassers or intruders could come into contact with the site.
• They could be reasonably expected to mitigate, minimise, or warn against any dangers.

The Occupier’s Liability Act is the primary law relating to trespassing at construction sites, and offers the most clarity through the above legislation on what your lawful obligations are. First issued in 1957, a revised 1984 edition followed the now-enshrined British Railways Boards vs Herrington in 1972, which first highlighted the need for property owners to owe a duty of care to trespassers after a young boy was severely injured on an improperly-secured railway line.

The Occupier’s Liability Act 1984 ensured more specificity and protection for both site owners and trespassers themselves. Part of that legislative clarity is of particular note for construction site operators, particularly those who are undertaking works in high-occupancy areas (such as ongoing new build housing estates, or city-centre renovations).

It allows property owners to be “discharged” of any liability if the trespasser willingly enters the site and is appropriately aware of the risks. That’s usually done through signage and fencing, but more conscientious principal contractors may opt to invest in temporary security technology as an additional deterrent.

This was best exemplified by Ratcliff vs McConnell in 1998. The occupier was found non-liable for the injury of a student who’d climbed over a 7-foot fence and jumped into an empty swimming pool, given that there were ample measures in place to warn of the danger and deter trespassing (i.e., the fencing and locked gate) and that the student could clearly see the present risks.

Liability is a serious consideration for construction site owners, as well as principal contractors and designers, and needs to be factored in as part of everyday considerations. The consequences of not doing so are often project-ending.

Supporting Legislation On Construction Site Trespassing

There are other pieces of legislation and guidance that offer clarity on what a construction site’s potential risks are when it comes to liabilities caused by trespassing and illegal site access. Chief among these is the Construction (Design and Management) Regulations 2015, or the CDM 2015.

As part of the CDM 2015 guidance on site security, site security is specifically mentioned, and must be implemented in a way that the public is protected from harm as much as is reasonably practicable. In practice, it sets out the need for site-specific solutions and security measures that work in tandem with ongoing developments, changing site plans, and both the design and construction phases.

That’s alongside strict regulations around health and safety, design and construction crossover, and more general guidance around the ability and competency of those working on the project. The CDM is one of the bigger legislative pieces governing construction, and it’s important to be as familiar with that as you are with the Occupier’s Liability Act 1984.

There’s also mention of this as part of the Health and Safety at Work Act 1974, which discusses a construction site’s responsibilities under criminal law to keep non-employees (including self-employed contractors, site visitors and trespassers) safe. This is often cited as part of the cases that relate to the Occupier’s Liability Act, and the two are closely linked.

What Could The Consequences Be If Someone Is Injured?

The consequences if someone is injured on your construction site can often be severe, particularly if you’re found to be in violation of the Occupier’s Liability Act 1984. This can range from costly project delays and uncapped fines to debarment from the trade and even jail time for serious breaches.

There are real-world examples of this. In the case of Jolley v. Sutton London Borough Council in 2000, the council was ordered to pay £621,710 (equivalent to £1.2 million in 2026) to a family whose child was injured while attempting to repair an abandoned boat that the council was aware of but failed to remove.

This is just a single example, with the private construction industry seeing countless more that are just as impactful from both a personal and a business perspective. A court case in February 2026 saw a construction firm fined over £183,000 due to improper protection on a roof, with a further court case in May 2025 seeing 4 men charged with corporate manslaughter after a woman died as a result of a pallet of bricks falling from a crane. 

Liquidation and administration are also a very real possibility, particularly if the fine is proportionate to the scale of the negligence at play. A small Hertfordshire construction firm went into liquidation earlier this year after a labourer died on what the HSE deemed a “death trap”. 

These are all consequences that can arise if your site isn’t properly secured, clearly signposted, and effectively mitigates the risks to trespassers, urban explorers and uninvited guests. It doesn’t touch on the potential loss of life and the wider ramifications of that, either, which can be a very real consequence of lax security.

We’d also point towards how these issues can reduce public faith in a company, especially if they’re picked up by local or national news outlets. All of the examples we’ve cited above are widely available, and anyone doing their due diligence in looking into the company undertaking their construction work may find these.

What Measures Do I Need In Place To Stop Trespassers Claiming?

As per Section 1(5) of the Occupier’s Liability Act 1984, you need to put appropriate measures in place to give warning of any dangers in place, and to discourage any trespassers or uninvited guests. That’s further supported by Section 1(6) of the Act, which removes any duty if there are adequate warnings in place and trespassers willingly choose to enter your site regardless.

For construction sites, this essentially means investing in effective, site-appropriate measures for security. These will vary based on a range of different factors, and as a first port of call, we’d recommend conducting a security site assessment that encompasses:

• Your project’s size and scale as it currently is
• Your project’s lifespan (and how that’s likely to affect the boundaries)
• Your ongoing risk factors (such as local crime rates or persistent issues)
• Your workforce, and how they come and go from the site
• Your vehicle traffic (and how that might change as the project progresses)
• Any adjacent occupied properties
• The location of site machinery, plant, or anything that may be of particular interest to trespassers (vacant properties, for example)

Smaller sites (usually self-contained construction projects that don’t occupy a larger space, or ongoing renovations at a domestic or small commercial property) will usually find that investing in adequate fencing and appropriate warning signage can suffice. This is usually Heras fencing, as it’s flexible and can be adapted if your site does need to change at any point.

For projects that are likely to have machinery left on site as part of their ongoing developments (civil works, for instance), temporary security technology can play an important role in removing liabilities and supporting necessary insurance claims if property is stolen, damaged or rendered unusable.

An AI-enhanced CCTV tower is our recommendation here. Not only does it function autonomously through solar power and an in-built battery, but it’s also an invaluable tool in mitigating claims made under the Occupier’s Liability Act. They’re designed to be a major deterrent, and integrated audio warnings offer additional support in that capacity.

They also function as an effective way to implement health and safety monitoring, which in turn reduces associated costs. Innovations in AI technology mean that modern CCTV towers also function as an automated check for standard construction site PPE (like hard hats and hi-vis clothing), which prompts an audio warning that the person is potentially unsafe.

These towers are one of the most cost-effective security investments available for larger sites, too. Their relative affordability and easy installation and decommissioning process ensure that large-scale developments that move at a rapid pace (think new-build housing estates, or inner-city developments like Manchester’s Crown Street) can also make effective use of towers alongside their existing security measures.

For even larger sites (major city-centre renovations or substantial governmental investment projects), we’d advise a blend of both those temporary technology solutions and a mobile manned security presence. This multi-pronged approach combines two of the most potent deterrents to trespassing and ensures value for money that intersects with legal compliance. 

It’s often what ProFM Group would advise as a trusted partner for dozens of construction companies across the UK. Site security solutions have to be built around your project, and that’s where our knowledgeable team and in-depth security assessment process earns its value.

We’re able to advise on the ideal spots for any temporary CCTV towers, how they can be most effectively utilised for monitoring and compliance with the Occupier’s Liability Act, and where manned guarding and security technology can merge for truly unique coverage of your construction project.

Get in touch with our in-house team today to book a site assessment and to receive a free quote that’s built to suit your project. There’s no obligation and no pressure – we know how complex compliance can be at the best of times, and our solutions are purpose-built to lessen those stresses.