Common Law powers of detention?

Just browsed the recent judgment in Clark v The Chief Constable of Merseyside Police [2023] EWHC 2565 (KB) and was a bit confused. It references “common law powers” for detaining people without specific lawful authority.

Interestingly it’s noted at Para 64 that the defence relied upon this and the Judge requested authority but the argument was later withdrawn. Then at Para 65 the Judge comments that

both parties agreed expressly that if the 09.59 decision was unlawful, taking into account the following matters numbered below, only nominal damages would be awardable. (1) The Claimant needed to be kept in a place of safety and the police were entitled to detain her under their common law powers.

I’m not sure how this makes sense. The Judge found that the detention was unlawful (and awarded nominal damages) but then also seems to accept submissions from both parties that the police were entitled to detain her.

The Claimant would not have been released had the correct common law power to detain been used in any event thus her situation would have been the same until her transfer for intensive mental health treatment to the Priory in the late afternoon the same day.

Is this per incuriam or am I missing something…

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Hadn’t heard of this case until you posted to this forum so have just read it through, once. I now have a list of questions but my instinct is this might be one of the weirdest judgments I’ve ever read.

• Mental Health Act 2003?
• What’s an “AMP”, precisely - “practitioner”?! - and is it really their job “only to complete the admission paperwork”?! WOW!
• Common Law powers? - without, as you say, mentioning anything about what they are. Is it the doctrine of necessity or something aout preventing a Breach of the Peace?
• States the claimant in police was “sectioned” a few days before when it seems most likely that we merely had medical recommendations.

What’s a “Place of Safety” got to do with it, given she was arrested for an alleged offence and never, at any stage, detained by the police under the MHA?!

I wonder how long the judge thinks these common law powers go on for, given locating a PICU bed can take days or weeks in some cases. Are they suggesting detention in custody for days is legal, because there’s no bed?!

This is actually very weird, in my view - thank goodness it’s merely the High Court and not binding, strictly speaking, on other courts or judgments.

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I decided to do a blog post on this. See if this summarises and prompts discussion -


That’s not quite what happened. Paragraph 64 was about the lawfulness of detention, and specifically an argument the police had made (then abandoned) that “because the common law power existed the arrest would have been lawful in any event”. Paragraphs 65-67 are about damages for the unlawful detention, nominal damages being awarded since the claimant “would not have been released had the correct common law power to detain been used in any event thus her situation would have been the same” (this is just the same approach as in Bostridge v Oxleas NHS Foundation Trust [2015] EWCA Civ 79).

This doesn’t answer the question about what the common law powers are, though! It would be interesting to hear from the lawyers involved in the case, as both parties agreed that the claimant “needed to be kept in a place of safety and the police were entitled to detain her under their common law powers”.

I wonder whether they had in mind R (Sessay) v South London and Maudsley NHS Foundation Trust [2011] EWHC 2617 (QB). That seemed to me an inconsistent judgment, in which the High Court said that (while the common law doctrine of necessity did not apply) “it is unlikely in the ordinary case that there will be a false imprisonment at common law or deprivation of liberty for the purposes of Article 5(1) ECHR if there is no undue delay during the processing of an application under ss.2 or 4 MHA for admission”. However, the court also said: “If a s.4 application cannot be completed without undue delay then the Trust’s staff may need to contact the police for them to consider using their powers of detention under s.136 MHA.” Michael’s conclusion is that:

In these situations, once an MHA application has been made (which it hadn’t, when the inspector conducted the second review), I’d be left thinking the detainee should be released and if doing so was considered “dangersouly to her and others” (para 65), then the grounds under s136 MHA would be met to justify removing the person to an actual Place of Safety under the MHA.

Using that approach, if there is no “no undue delay”, could the common law (lack of false imprisonment) have covered the time between the unlawful 0959 decision and the MHA application? Or would the correct approach instead to use s136 as soon as it was available, without waiting for the MHA application?

The judge said:

  1. … He only completes the admission paperwork if two consultant psychiatrists have concluded the detainee needs to be admitted for treatment. …

I think he is just using “only” in the “only can do x if y” sense, not in any pejorative way. That sentence on its own does make the outcome seem a foregone conclusion, but some more of the AMHP’s role had been described earlier in the judgment:

  1. … Mr Sandhu arrived at around 3pm and was satisfied that the Claimant needed to be detained under the MHA 1983 but likewise did not consider the Claimant was a medical emergency. …

  1. … Ms McDonnell had started the process of getting the AMP to come to the station to have the Claimant admitted and to source a mental health bed before 09.59.

Yes, the “forgone conclusion” aspect being my concern - I could have written that more clearly. It’s almost as if he didn’t countenance the AMHP contemplating any other approach than just signing the paperwork.

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At first sight it is strange that the judge accepts that, once the PACE detention can no longer be justified, Ms Clark can continue to be held under common law (necessity, I assume) for her own safety and that of others pending a MHA application. As Michael says, this appears to be open-ended.

The key I think is that the facts occurred in 2016, i.e. before the changes to s.136 in the Policing and Crime Act, when common law necessity was regularly cited as a defence to false imprisonment. If the same situation occurred today, I don’t think it could be justified, because Ms Clark could now be transferred to a place of safety under s.136- indeed, as Michael knows well, that is expressly set out in the police Authorised Professional Practice on mental disorder as an appropriate option in these circumstances. My understanding is that common law cannot be relied upon if a statutory provision is available which achieves the same outcome.

Whether space would be available in a hospital-based place of safety is another matter!