Construction Site Security UK: Legal Duties Guide

At a glance

• Core statutory duty: CDM 2015, regulation 13(4)(b) requires the principal contractor to ensure "the necessary steps are taken to prevent access by unauthorised persons to the construction site."
• Every contractor is bound too: regulation 15(10) prevents any contractor from beginning work on site unless reasonable steps have been taken to prevent unauthorised access.
• Perimeter standard: regulation 18 requires a site to have its perimeter identified by suitable signs and be arranged so its extent is readily identifiable, or be fenced off, so far as is reasonably practicable and proportionate to the risk.
• Duty to the public generally: section 3 of the Health and Safety at Work etc. Act 1974 requires an undertaking to be conducted so that, so far as is reasonably practicable, people who are not employees (including passers-by, neighbours, and trespassers) are not exposed to risk.
• Duty to lawful visitors: the Occupiers' Liability Act 1957 imposes a "common duty of care" on occupiers towards anyone lawfully on site, including delivery drivers, inspectors, and clients.
• Duty to trespassers, including children: the Occupiers' Liability Act 1984 can require an occupier to take reasonable precautions where they know or ought to know a danger exists and that someone, especially a child drawn in by an "allurement" such as machinery or an excavation, may come near it.
• Manned guarding: third-party security guards generally need an SIA licence under the Private Security Industry Act 2001, unless they are employed directly, in-house, by the site operator.

What is construction site security, legally speaking?

Construction site security covers the physical, procedural, and organisational steps taken to stop unauthorised people entering a site, to protect plant and materials from theft or damage, and to reduce the risk of accidents involving trespassers, especially children. It is not a single legal requirement sitting in one place.

Instead, it flows from a combination of general workplace safety law, construction-specific regulations, the common law duty of care owed to visitors and trespassers, and, increasingly, the conditions attached to insurance policies covering the works. In practical terms, security on a construction site usually involves perimeter protection, controlled entry, lighting, signage, surveillance, and clear procedures for everyone working on or visiting the site.

The level of security expected is proportionate to the risk: a small domestic extension in a suburban street will not need the same measures as a major city centre development running around the clock. What matters, under each of the legal duties below, is that the person in control of the site has thought about the risks and taken reasonable, or reasonably practicable, steps to address them.

This guide covers England and Wales.

The statutory duties that drive site security

CDM 2015: the construction-specific framework

The Construction (Design and Management) Regulations 2015 (CDM 2015) is the main construction-specific regime, and it addresses site security directly in three places:

• Regulation 13(4)(b) requires the principal contractor to ensure that "the necessary steps are taken to prevent access by unauthorised persons to the construction site." This sits alongside the principal contractor's wider duty in regulation 13(1) to plan, manage, and monitor the construction phase so that work is carried out, so far as is reasonably practicable, without risks to health or safety.
• Regulation 15(10) places a parallel duty on every individual contractor: a contractor "must not begin work on a construction site unless reasonable steps have been taken to prevent access by unauthorised persons to that site." This means the obligation does not rest solely with the principal contractor. Any contractor mobilising onto an insecure site is itself in breach.
• Regulation 18 sets the physical standard: so far as is reasonably practicable, and in accordance with the level of risk, a construction site must either have its perimeter identified by suitable signs and be arranged so its extent is readily identifiable, or be fenced off. This is the provision that underpins the common practice of hoarding busy urban sites and using mesh fencing with clear signage on lower-risk sites.

On most commercial projects, these roles (client, principal designer, principal contractor, and contractor) are formally assigned under CDM 2015. On smaller domestic projects, a single contractor may be treated as the principal contractor if no one else has been appointed to the role.

HSWA 1974: the general duty to the public

Away from construction-specific rules, the Health and Safety at Work etc. Act 1974 imposes broader duties that also bite on site security:

• Section 3 requires every employer and self-employed person to conduct their undertaking so that, so far as is reasonably practicable, people who are not their employees and who may be affected by it are not exposed to risks to their health or safety. This is the provision that captures neighbours, passers-by, and trespassers who are put at risk by an insecure site.
• Section 4 places duties on anyone with control of non-domestic premises, or of the means of access to or egress from them, to take reasonable measures to ensure those premises and access routes are safe for people using them.

Occupiers' liability: the civil law layer

Alongside the regulatory duties, occupiers' liability law governs civil claims if someone is injured:

• The Occupiers' Liability Act 1957 imposes a "common duty of care" on occupiers towards lawful visitors, meaning the site must be reasonably safe for the purpose the visitor was permitted to be there. The Act specifically notes that an occupier "must be prepared for children to be less careful than adults."
• The Occupiers' Liability Act 1984 can extend a duty of care to people who are not lawful visitors, including trespassers. Under section 1(3), a duty arises where the occupier is aware of a danger (or has reasonable grounds to believe it exists), knows or has reasonable grounds to believe someone may come near it, and the risk is one the occupier could reasonably be expected to guard against. This is the basis of the "allurement" principle often discussed in relation to construction sites: attractive but dangerous features, such as unsecured excavations, exposed reinforcement, cranes, or plant, are more likely to draw in children, and courts have historically treated that foreseeability as raising the standard expected of the occupier.

SIA licensing for manned guarding

If the site uses a third-party security company for manned guarding, the individual guards will usually need a licence under the Private Security Industry Act 2001. Licensable activities include guarding premises against unauthorised access, disorder, or damage. There is a long-standing exemption for in-house security staff employed directly by the company operating the site, but contracted guarding companies must hold and display the correct SIA licence while working — see GOV.UK's guidance on when you need an SIA licence.

Key steps to a legally compliant approach

1. Identify who carries the legal duty. Work out who is the client, the principal contractor, the principal designer, and any other duty holders for the project under CDM 2015. Clarity on who is responsible for site security from day one helps avoid gaps later, particularly given that both the principal contractor (regulation 13) and each individual contractor (regulation 15) carry an unauthorised-access duty.
2. Assess the specific risks for your site. Consider the location, the nature of the work, neighbouring properties, public footpaths, schools nearby, hours of operation, and the value of plant and materials on site. A written risk assessment should record what you have considered and why certain security measures have been chosen, in line with the "reasonably practicable" and risk-proportionate standard used throughout CDM 2015, and it should be revisited as the project progresses.
3. Put physical security measures in place that meet regulation 18. This typically means hoarding or fencing of a suitable height and strength, gated access points, secure storage for tools and materials, and adequate lighting at night. On urban sites, solid hoarding is usually expected. On more remote, lower-risk sites, mesh fencing with anti-climb measures and clear perimeter signage may be enough, depending on the risk assessment.
4. Control who comes on site and when. Use a single monitored entry point where possible, sign-in and sign-out procedures, identification checks for visitors, and induction briefings for anyone new to site (CDM 2015 regulation 13(4)(a) specifically requires a suitable site induction). Out of hours, the site should be locked down, with keys and access codes held only by those who need them. Record keeping helps if an incident later needs investigating.
5. Check any manned guarding is properly licensed. If you use a third-party security provider, confirm its guards hold a valid SIA licence under the Private Security Industry Act 2001 and display it while on duty. If security is provided in-house by your own employees, the licensing exemption will usually apply, but check the current GOV.UK guidance if the arrangement is not straightforward.
6. Review, record, and respond to incidents. Keep a log of near misses, break-ins, thefts, and public safety concerns. Review your security arrangements after any incident and after each major phase of works. Report serious incidents to the police and, where relevant, to the Health and Safety Executive. Ongoing review is what separates a site that stays secure from one that only looked secure on paper.

Practical measures that map to the legal duties

• Hoarding and fencing: matched to the risk assessment required to satisfy CDM 2015 regulation 18 — solid hoarding for busy urban frontages, mesh fencing with anti-climb features for lower-risk perimeters.
• Signage: perimeter and access-point signs identifying the site, the principal contractor, and any CCTV in operation, supporting both regulation 18 and the general duty under HSWA 1974 section 3 to warn people who may be affected by the works.
• Securing plant, excavations, and materials out of hours: directly relevant to the Occupiers' Liability Act 1984 "allurement" risk for children and to the ongoing duty under CDM 2015 regulations 13 and 15, which are not limited to working hours.
• Controlled access and induction: required by CDM 2015 regulation 13(4)(a) and supports the section 4 HSWA duty to keep means of access and egress safe.
• CCTV, alarms, and licensed guarding: commonly used to evidence that reasonable steps were taken, with any contracted guards holding a valid SIA licence under the Private Security Industry Act 2001.

This guide provides general information about the legal duties relevant to construction site security in England and Wales. It is not legal advice and is not a substitute for advice tailored to your specific project. If you are weighing up your obligations on a current or upcoming project, consider taking advice on your specific circumstances.

Last reviewed: July 2026 by a non-practising solicitor · Next review due: July 2027 or on legislative change.