A guide for litigants in person on the two hurdles every lawful arrest has to clear — and why the reason an officer gives you at the time is the only one that counts.
Most people believe that if a police officer “had their suspicions”, the arrest was lawful. It is one of the most common misunderstandings litigants in person carry into a wrongful-arrest claim. The truth is that suspicion, on its own, decides almost nothing. An officer can suspect you sincerely, and even reasonably, and the arrest can still be unlawful.
That is because a lawful arrest under English law has to climb two separate hurdles, not one. First, the officer needs reasonable grounds to suspect you of an offence. Second — and this is the part almost everyone misses — the officer needs reasonable grounds to believe that arresting you is necessary. Clearing the first hurdle does nothing for the second. And running underneath both is a third rule, about what you must actually be told.
If you are challenging an arrest, knowing where those hurdles sit is the difference between a vague sense of unfairness and a claim a court can act on. Here is what the law actually requires.
Suspicion is not a hunch
The power to arrest without a warrant comes from section 24 of the Police and Criminal Evidence Act 1984 (PACE). It starts with suspicion — but “reasonable suspicion” is a legal test with two halves, and the police have to satisfy both.
The leading case is O’Hara v Chief Constable of the Royal Ulster Constabulary [1997] AC 286, decided in the House of Lords. It splits reasonable suspicion into two parts:
- A subjective part. The officer must actually suspect you. Not “might have done”; not “could have done, looking back”. The suspicion has to have existed in that officer’s own mind at the moment of arrest.
- An objective part. There must be reasonable grounds for that suspicion. A court, looking at what the officer knew, must be able to say the suspicion was reasonable rather than fanciful.
The older Court of Appeal decision in Castorina v Chief Constable of Surrey (1988) puts the same idea as three questions: did the officer suspect? were there reasonable grounds for that suspicion? and, if so, did the officer then exercise the discretion to arrest properly? Both cases land on the same point — a feeling is not enough. There has to be material the officer can point to.
Two things are worth holding onto here, because they cut both ways. Those grounds do not have to amount to proof, and they do not even have to turn out to be correct. An arrest is not made unlawful simply because you were later released without charge or acquitted. The question is whether, on the information the officer genuinely had at the moment of arrest, the suspicion was reasonable. Hindsight does not help you, and it does not rescue the police either.
“But my neighbour told them I did it”
A complaint can give an officer reasonable grounds — but a bare accusation, standing entirely alone, often will not. This matters enormously in the kinds of disputes litigants in person are usually caught up in: neighbour rows, alleged harassment, family fallings-out, accusations at work.
O’Hara settled a closely related point. An officer can form reasonable suspicion on information passed to them by someone else — a briefing, a colleague, a member of the public. What an officer cannot do is arrest purely because they were ordered to. A bare instruction — “go and arrest him” — with nothing in the arresting officer’s own mind to justify it, does not amount to reasonable grounds. The officer who makes the arrest has to have something, even if that something originally came from someone else.
Likely lawful: A shopkeeper tells an officer they watched you on CCTV slip an item into your bag and walk out without paying, and points to the footage. The officer now has a named witness, a specific account, and a source they can check. That is material; the suspicion is reasonable.
Likely unlawful: In a long-running neighbour dispute, an officer arrests you only because a sergeant said “she’s the one, bring her in”, and at trial the officer can give the court no information of their own about what you are actually supposed to have done. There may be suspicion in the sergeant’s mind, but not in the arresting officer’s. The first hurdle is not cleared.
Even with grounds, the arrest can still be unlawful
Here is the hurdle that catches the police out most often, and the one litigants in person most often overlook. Since the law was tightened in 2005 (in force from 1 January 2006), section 24 PACE requires more than suspicion. The officer must also have reasonable grounds to believe that the arrest is necessary — and necessary for one of a specific, closed list of reasons set out in section 24(5).
The leading authority is Hayes v Chief Constable of Merseyside Police [2011] EWCA Civ 911; [2012] 1 WLR 517. Hughes LJ laid down a two-stage test for necessity:
- the officer must honestly believe that the arrest is necessary, for one or more of the section 24(5) reasons; and
- that belief must be objectively reasonable — a court, on the facts, must be able to agree it was a reasonable belief to hold.
The section 24(5) reasons are a fixed list. In plain terms, arrest must be necessary to: establish the person’s name or address; stop them causing injury to themselves or someone else, or damage to property; protect a child or other vulnerable person; allow the prompt and effective investigation of the offence or of the person’s conduct; or prevent a prosecution being frustrated by the person disappearing. The fourth of those — “prompt and effective investigation”, section 24(5)(e) — is the reason officers reach for most often, and it is the one most often stretched past breaking point.
The courts treat necessity as a genuinely high bar, not a box to tick. It means more than convenient, more than desirable, more than tidy. The case law is blunt about it: an officer who has given no real thought to the alternatives to arrest risks a finding that they had no reasonable grounds for believing arrest was necessary at all. If the arrest could just as easily not have happened, it probably was not necessary.
This is the heart of the myth. Suspicion gets an officer to your door. Necessity is what lets them take you through it.
If you went in voluntarily
This is where a great many arrests fall apart, and it speaks directly to anyone who agreed to “come in for a chat”.
In Richardson v Chief Constable of West Midlands Police [2011] EWHC 773 (QB), a teacher of good character, accused of assaulting a pupil, attended a police station voluntarily, by arrangement, with his solicitor. He was arrested anyway. Slade J held the arrest unlawful. Before arresting, the officer had to consider whether arrest was actually necessary, or whether a voluntary interview — which was exactly what the man had turned up to give — would achieve the same objective. Where someone is cooperating and is present of their own free will, arresting them “to investigate” is very hard to justify: you can simply interview them.
Richardson also makes a point that catches forces out repeatedly. The custody officer’s later reasons for authorising detention are a separate exercise; they do not cure a defect in the arrest itself. If the arrest was unlawful when the officer made it, a sensible-sounding authorisation a few minutes later at the custody desk does not retrospectively make it lawful.
Likely unlawful: You get a call asking you to attend the station about a harassment allegation. You go in, on time, no fuss, ready to answer questions, and you are arrested at the front desk. Unless the officer can show why arrest — rather than the voluntary interview you turned up for — was necessary, that arrest looks like Richardson.
Likely lawful: You are repeatedly asked to attend, you ignore the appointments, and there is genuine reason to think you will warn a witness or destroy evidence if left at large. Now “prompt and effective investigation”, or preventing your disappearance, may make arrest genuinely necessary.
Necessity is always fact-specific. But voluntary cooperation is powerful evidence against necessity — and the police know it.
The reason has to be given at the time
The third rule sits underneath everything above. You must be told why you are being arrested, at the time it happens.
The classic authority is Christie v Leachinsky [1947] AC 573, in the House of Lords: a person must be told the true ground for their arrest at the time, or as soon as is reasonably practicable. This is now reinforced by section 28 PACE, which states in terms that an arrest is not lawful unless the person is informed that they are under arrest and told the ground for it.
The deeper principle is the one that defeats after-the-fact justification. An arrest is judged on the reason that was operating at the time — not on a better reason the police think of later. They cannot arrest you for one thing, find that it does not hold up, and then prop up the very same arrest on a different ground invented afterwards to plug the gap. The lawfulness of the arrest is fixed at the moment it is made.
Likely unlawful: You are arrested and told only “you know why”, with no ground given. Months later, a carefully drafted witness statement sets out tidy reasons. Those reasons came far too late; under Christie and section 28 the arrest was unlawful from the start, and the statement cannot reach back and fix it.
Likely lawful: At the moment of arrest you are told you are being arrested on suspicion of a specific offence and given the gist of why. That is the ground — and it is the one, and the only one, the court will test.
Who has to prove what
One last point, because it changes how a litigant in person should think about the whole thing. In a claim for wrongful arrest and false imprisonment, the burden is not on you to prove the arrest was unlawful in the way you might expect. It is for the police to justify the arrest. That was treated as common ground in Hayes: the force has to show it cleared the hurdles.
False imprisonment is also actionable without you having to prove any particular loss — the unlawful detention is the wrong in itself. And, crucially, you do not have to prove you were innocent of whatever you were suspected of. Guilt or innocence is a different question entirely. An arrest can be unlawful even if you did exactly what was alleged, and lawful even if you did nothing at all. The two issues do not touch.
Putting it together
When you look back at your own arrest, test it against three things, in order:
- Suspicion. Did the arresting officer actually suspect you, on grounds a court could call reasonable? (O’Hara; Castorina)
- Necessity. Did the officer have reasonable grounds to believe arrest was necessary for a specific section 24(5) reason, having genuinely considered the alternatives — above all, a voluntary interview? (Hayes; Richardson)
- Communication. Were you told the true ground at the time — and is the force now relying on that same ground, rather than a better one invented later? (Christie v Leachinsky; section 28 PACE)
An arrest has to pass all three. Fail any one of them and it may be unlawful, opening the door to a claim for false imprisonment regardless of whether you were guilty of anything.
So the next time an officer — or a defence in a witness statement — says they “had reasonable grounds”, treat it as the beginning of the question, not the end of it. Suspicion gets an officer to your door. Necessity is what lets them take you through it — and the only reason that counts is the one they give you at the time.
