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

As one of the most at-risk premises for trespassing and unauthorised access, construction sites raise a question many principal contractors haven’t had answered clearly, which is what’s expected of you under the law if someone who trespasses on your site is injured.

In England and Wales, construction site trespassing can still lead to a claim.

The duty you owe is limited, though, and can be met with a few steps.

Your challenge, is knowing what counts as enough to cover yourself, so this article covers the law, the measures that support it and the records that prove it.

For a broader read on security, check out our construction site security guide.

Is Trespassing On Construction Sites Illegal?

Technically, what you’d call “illegal trespassing” is a civil matter when dealt with on its own.

In England and Wales, someone going onto your site without permission is generally not a criminal offence so there’s no automatic arrest, criminal record or set fine for trespass alone.

It becomes a criminal matter if and when the person does something else.

Damaging fencing or plant is criminal damage under section 1 of the Criminal Damage Act 1971.

Entering a building as a trespasser to steal or cause damage is burglary under section 9 of the Theft Act 1968.

And trespassing to disrupt lawful work can be aggravated trespass under section 68 of the Criminal Justice and Public Order Act 1994.

None of that takes away your duty of care for anyone on your site.

Whether you’re dealing with thieves, curious children or urban explorers, you can still owe that duty of care if someone’s injured.

What Does The Law Say About Construction Site Trespassing?

Under section 1 of the Occupiers’ Liability Act 1984, property owners and occupiers can owe a “duty of care” to trespassers and uninvited visitors, even if they arrive while the property owner isn’t present. That duty isn’t automatic. It also covers personal injuries rather than property damage. Under section 1(3), it applies only where all three of these conditions are met:

1. They’re aware of the danger at the site or have reasonable grounds to believe it exists
2. They know, or have reasonable grounds to believe, the person is in a dangerous area or may come into it.
3. They could be reasonably expected to offer the person some protection against the risk, taking everything into account.

The Occupiers’ Liability Act 1984 is the primary law relating to trespassing at construction sites and is separate from the Occupiers’ Liability Act 1957, which covers lawful visitors.

It allows property owners to be “discharged” of their duty under section 1(5), in an appropriate case, if they take reasonable steps to warn of the danger or to discourage people from facing the risk.

Section 1(6) removes the duty for risks a person has willingly accepted.

If you’re in Scotland or Northern Ireland, they have their own occupiers’ liability law that you’ll need to look into.

Supporting Legislation On Unauthorised Access To Construction Sites

There are other pieces of legislation and guidance that offer clarity on the liabilities that trespassing and unauthorised access can create. Chief among these is the Construction (Design and Management) Regulations 2015 and (CDM 2015), which we’ve covered in our guide to CDM 2015 and site security.

If you’re the client, regulation 4 requires suitable project arrangements, which you must take reasonable steps to make sure your principal contractor meets its duties. The Health and Safety Executive (HSE) also expects you to supply information on boundaries and access control.

Under regulation 13(4)(b), the principal contractor has to ensure necessary steps are taken to prevent unauthorised people accessing the site.

On a project with several contractors, that makes site security the principal contractor’s day-to-day responsibility (and hiring a security provider doesn’t transfer it, since their reports feed into your own monitoring).

Under regulation 15(10), if you’re a contractor, you must take reasonable steps to prevent unauthorised access before you start work, including on smaller projects.

Children, Vulnerable People And Construction Site Safety

Children are singled out by the HSE as a group that needs particular protection against construction sites, because many see active sites as fun places to play. Their protecting the public guidance says you must do everything you can to keep kids out and away from danger.

The same goes for elderly people and people with certain disabilities.

In Jolley v Sutton London Borough Council in 2000, a 14-year-old was injured while working beneath an abandoned boat that children had been messing with. The House of Lords accepted the risk of children meddling with it and being hurt was foreseeable, even though the exact accident wasn’t.

It isn’t a construction site case, but it shows how a court views the issue.

In June 2026, HSE urged construction companies to strengthen site security ahead of the school holidays, highlighting steps you can take:

• Suitable perimeter fencing or hoarding, checked regularly
• Securing the site at the end of each working day
• Barriers or covers over excavations and pits
• Plant and vehicles isolated and immobilised
• Materials stored so they can’t topple or roll
• Access ladders removed from scaffolds and excavations
• Hazardous substances locked away

What Could The Consequences Be If Someone Is Injured?

The consequences if someone is injured on your construction site can often be severe and can go two ways.

First is a civil claim for damages under the 1984 Act, which means compensation rather than a fine. The second is prosecution under the Health and Safety at Work etc. Act 1974 and CDM 2015, which can bring unlimited fines for organisations and, in qualifying cases, prison time for the relevant people.

In July 2020, 10-year-old Shéa Ryan and other children got into a construction site in Drumchapel through an insecure fence. He died after falling more than 6 metres down a manhole.

The principal contractor, RJ McLeod (Contractors) Limited, pleaded guilty to a health and safety breach and was fined £800,000 in April 2023 after the Crown Office and Procurator Fiscal Service said it had no formal written system for monitoring damage to its perimeter fencing.

The cost isn’t only legal. An incident can also affect your insurance, so check your policy for any conditions on site 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.

What Site Security Measures Do I Need In Place

As per Section 1(5) of the Occupiers’ Liability Act 1984, you can complete your duty of care, in an appropriate case, by taking reasonable steps to warn of any danger and discourage people from going near the risk. The test is whether it’s deemed reasonable.

Start With A Site Assessment

The right measures will vary with your site, and as a first port of call, we’d recommend conducting a security site assessment as part of your construction site security plan, which can include:

•       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)

Measures For Preventing Trespassing: Fencing And Signage

Smaller sites will usually find that investing in adequate fencing and appropriate warning signage is where to start. This is usually Heras fencing, as it’s flexible and can be adapted if your site does need to change.

HSE’s baseline for your site in a populated area is typically a two metre high small-mesh fence or hoarding. Its HSG151 guidance adds that mesh should give no handholds or footholds, sections should be locked together and gaps underneath kept as small as possible. Where children have already tried to get in, larger hoardings may be needed.

In our experience, warning signs – the ones that name the specific danger, not just “Keep Out” – carry more weight.

When To Add CCTV Systems

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 add to your physical measures and support any insurance claim if property is stolen, damaged or rendered unusable.

It won’t remove your liability, though, and CCTV systems alone don’t remove the duty.

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 designed as a visible deterrent, with integrated audio warnings adding to it.

Innovations in AI technology mean that modern CCTV towers also function as an automated check for standard construction site personal protective equipment like hard hats and hi-vis clothing, which prompts an audio warning that the person is potentially unsafe.

Larger Sites: Towers And Mobile Patrols

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 visible deterrents to trespassing, and the patrol records feed into your own monitoring. Our guide to mobile patrols or static guarding explains how to choose between them.

We’re able to advise on the ideal spots for any temporary CCTV towers, how they can be most effectively utilised for monitoring and where manned guarding and security technology can merge on your project. If you’d like a second opinion, you can book a site assessment with our team.

What Evidence Protects You After An Incident?

Section 1(5) depends on whether steps you took were reasonable in all the circumstances and you can provide any evidence when asked.

Having a fence installed is one thing, but you may need records of inspections, photographs and patrol logs to show it was the right type, intact and repaired quickly when needed.

The law doesn’t have a standard defence and CDM 2015 doesn’t outright require a standalone site security log.

But it does require a construction phase plan that’s reviewed and updated throughout your project (under regulation 12) and employers with five or more employees have to record significant findings of their risk assessment, under regulation 3 of the Management of Health and Safety at Work Regulations 1999.

The records worth keeping include:

•       A dated risk assessment for unauthorised access, including previous breaches

•       Dated photographs of fencing, gates and signs, with the original files kept

•       Inspection logs showing who checked, when, what they found and what was repaired

•       CCTV tower and patrol logs, including detections, response times and checkpoint visits

•       Breach reports that close out with a verified repair

Practical Site Safety Support From ProFM Group

Start by assessing your site against the factors above. This article is general guidance, not legal advice, so please speak to a solicitor about your own circumstances.

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 construction site security services are built to take some of that weight off.

We’re a Security Industry Authority (SIA) Approved Contractor, our officers are vetted to BS7858 (the British Standard for security screening) and our CCTV monitoring holds National Security Inspectorate (NSI) Gold approval.