Intruders, Trespassers, and ‘Chancers’: A Guide for UK Security

For security officers, knowing your legal boundaries is as crucial as knowing how to handle a physical threat. Misunderstandings about powers can lead to serious legal trouble. What’s the difference between a trespasser and a burglar? How much force is ‘reasonable’? When can you actually make a citizen’s arrest?

This guide offers a plain-English overview of the legal basics every UK security officer needs to know to act confidently and lawfully when faced with intruders, trespassers, and opportunistic ‘chancers.

Trespass vs. Burglary: What’s the Legal Difference?

It’s easy to use these terms interchangeably, but in the eyes of the law, they are very different. Getting it right is vital for your incident reports and how you justify your actions.

Trespass is a civil matter, not a criminal one. It happens when someone enters or remains on private property without permission. For more detail, see the UK Government guidance on trespass. For example, a group of youths cutting across a construction site after hours is trespassing. While you can ask them to leave and use reasonable force to remove them if they refuse, the police are unlikely to intervene unless another crime is committed.

Burglary, on the other hand, is a serious criminal offence under the Theft Act 1968. It involves entering a building (or part of a building) as a trespasser with the intent to steal, inflict grievous bodily harm, or cause unlawful damage. If someone forces a door on a retail unit after closing time, that’s no longer simple trespass; it’s burglary. The intent is what elevates the act to a crime police will investigate.

What is ‘Reasonable Force’?

The term ‘reasonable force‘ is central to a security officer’s role, but it has no exact legal definition because it is entirely dependent on the situation. Section 3 of the Criminal Law Act 1967 allows anyone to use such force as is reasonable in the circumstances to prevent a crime or assist in a lawful arrest.

So, what does this mean in practice? It means your response must be proportionate to the threat you face.

  • Proportionality is key: Using a firm arm-hold to escort a disruptive but non-violent person from a venue is likely reasonable. However, tackling them to the ground would be excessive.
  • It’s judged on the ‘heat of the moment’: The law recognises that in a stressful, fast-moving situation, you can’t be expected to measure the precise amount of force needed. If you honestly believed the force was necessary to protect yourself, someone else, or property, your actions are more likely to be considered lawful (see CPS guidance on reasonable force).
  • Excessive force has consequences: If you continue an attack after the danger has passed or use a level of force far beyond what was required, you could face criminal charges for assault. Your actions must always be justifiable.

Performing a Citizen’s Arrest

As a security officer, you have the same power as any other member of the public to perform a citizen’s arrest under Section 24A of the Police and Criminal Evidence Act 1984 (PACE). However, this power comes with strict conditions.

You can only perform a citizen’s arrest for an indictable offence (a more serious crime, like burglary or assault). You must also have reasonable grounds for believing that the arrest is necessary for one of the following reasons:

  • To prevent the person from causing physical injury to themselves or others.
  • To prevent them from causing loss of or damage to property.
  • To prevent them from making off before a constable can assume responsibility.

Crucially, you must have witnessed the crime or have reasonable grounds to believe the person is in the act of committing it. You cannot arrest someone because you think they committed a crime yesterday. If you do make an arrest, you must contact the police immediately and only detain the individual for a reasonable period—that is, until the police arrive. For official guidance, review the PACE Code G.

Spotting ‘Suspicious Entry’

Knowing what constitutes ‘suspicious entry’ depends heavily on your environment. What’s normal in one setting is a major red flag in another.

  • Venues and Events: Look for individuals trying to bypass ticket checks, using fire exits to let others in, or loitering in restricted ‘staff only’ areas. Their behaviour may be a precursor to theft or causing trouble.
  • Construction Sites: Anyone on site outside of working hours without authorisation is suspicious. Pay attention to people testing fences, observing the site from a distance over several days, or carrying tools near the perimeter. This could indicate plans for theft of materials or machinery.
  • Retail: Be alert for individuals who avoid staff, seem more interested in CCTV cameras than products, or work in groups to distract employees. Carrying large, empty bags can also be a sign of a potential shoplifter.
  • Residential Blocks: ‘Chancers’ often test communal doors to see if they’re unlocked. Tailgating—slipping in behind a resident—is a common tactic. Anyone trying multiple apartment doors or loitering in hallways without a clear purpose warrants immediate attention.

When you encounter suspicious activity, your first steps should be to observe and report. Approach calmly, identify yourself, and ask questions to determine if they have a legitimate reason to be there. Your goal is to de-escalate and deter, not to immediately confront.

Your Rights and Limitations as a Security Officer

Knowing what you can and cannot do is essential for operating legally and professionally.

What you CAN do:

What you CANNOT do:

  • Act as a police officer. You do not have police powers (police powers overview).
  • Search someone or their property without consent. This is assault and a breach of their rights (UK Government: Stop and search).
  • Use handcuffs unless you have been properly trained and their use is necessary and proportionate to the situation. Their misuse can lead to serious charges.
  • Use excessive force. Your actions must always be justifiable (CPS: Use of force guidance).
  • Confiscate property unless you believe it to be stolen evidence as part of a lawful citizen’s arrest, to be handed over to the police.

Staying Legally Sound

Your work is governed by a framework of laws, including the Criminal Law Act 1967 (on reasonable force), PACE 1984 (on arrest), and standards set by the Security Industry Authority (SIA). Furthermore, the Human Rights Act 1998 protects an individual’s rights, and the Data Protection Act 2018/GDPR governs how you handle any data you collect, including CCTV footage.

Real-World Scenarios

  • Scenario 1: The Loiterer. You see a man trying door handles in a residential block. He hasn’t entered anywhere yet. Action: Approach, identify yourself, and ask his purpose. His response will dictate your next move. If he becomes aggressive or tries to force a door, it may escalate to an attempted crime, justifying a call to the police (how to contact the police).
  • Scenario 2: The Refused Search. At a festival gate, a man refuses to let you search his bag. Action: You cannot force the search. You can, however, refuse him entry as it’s a condition of the ticket. Politely explain this and ask him to leave the queue (SIA search rules).
  • Scenario 3: The Shoplifter. You witness a woman put an expensive item in her bag and walk past the tills. Action: This is theft. You have grounds for a citizen’s arrest. Approach her calmly after she has left the store, state who you are, and inform her she is being detained on suspicion of theft until the police arrive (Theft Act 1968).

Your Professional Duty

Understanding the legal basics is not just about avoiding lawsuits; it’s about being a more effective, professional security officer. It allows you to make smart, justifiable decisions under pressure, protecting yourself, the public, and the property you are hired to secure.

Always keep your knowledge current. When in doubt, de-escalate, observe, and report. Your primary role is to be a deterrent and a safe presence, and that starts with knowing the law.