Here we are, more than a decade in to this blog, almost 1,000 posts about various topics and a question came up today which I instantly knew we hadn’t covered – because it doesn’t come up very often at all.
There’s loads of law in this one, so ensure you have a hot, sweet beverage or some painkillers on hand. But the punchline here is simple, so just push through and it will all make sense at the end!
Two quick reminders first —
- A section 2 Mental Health Act (MHA) patient can be detained in hospital for up to 28 days once they arrive in hospital. During that time, they are detained for assessment of their condition and for subsequent decisions to be made about treatment and the 28 day period cannot be extended to allow for a longer period of assessment – or can it?! … hold that thought.
- A section 3 MHA patient can be detained for up to six months in hospital for treatment of their condition and that detention can be extended for a further six month period and then for subsequent twelve month periods. In theory, the s3 order can be extended many times and someone detained for years, albeit there are checking mechanisms in the law to oversee all of that.
But what happens if the person goes missing from hospital just prior to their period of detention ending and they remain absent without leave at the point where the s2 or s3 order runs out? – this post refers to someone who goes missing in the final week of their detention under either of these order.
REAL WORLD SITUATION
So the question raised to me was —
A s2 MHA patient has been in hospital for 26 days at the point where they abscond from the ward one morning. Arrangements were in hand to further assess them under the MHA in the afternoon for detention under s3 MHA, but the absconding prevented the s3 assessment / application being completed. The police begin a missing person’s investigation but none of the obvious enquiries reveal the patient’s whereabouts before the 2 order runs out. A few days went by and on day 30 after admission, enquiries reveal the patient’s location —
Exam question: can the police re-detain this patient under section 18 MHA and return them to hospital? … section 21 was mentioned, as being mechanism which allows an extra seven days for re-detention.
You may not have heard of s21 MHA because it rarely comes up and one reason is it’s mostly for hospitals to care about, not for the police or for anyone else doing the re-detaining (because remember, staff on the hospital, Approved Mental Health Professionals and anyone authorised by the hospital can also re-detain under s18 MHA!) But s21(1) MHA states that where a patient is absent without leave on the day they would cease to be ‘liable to be detained’, they will not cease to be liable until the “relevant time”.
RELEVANT TIME
So understanding the “relevant time” is obviously key! What’s that getting at? —
Section 21(2) —
(a) where the patient is taken into custody under section 18 above, is the end of the period of one week beginning with the day on which he is returned to the hospital or place where he ought to be;
(b) where the patient returns himself to the hospital or place where he ought to be within the period during which he can be taken into custody under section 18 above, is the end of the period of one week beginning with the day on which he so returns himself; and
(c) otherwise, is the end of the period during which he can be taken into custody under section 18 above.
You’ll notice that all of this applies to situation where someone has been or could be taken in to custody under s18 MHA – in other words, people who can still be re-detained. For s2 MHA patients, we know re-detention can only occur in the original 28-day period after admission – see s2(4) and s18(5) MHA for confirmation of this. So to answer the exam question: NO – you cannot re-detain someone who was found 30 days after their original s2 MHA hospital admission. You’d either need to the police to use s136 MHA (if the grounds for doing so were met) or an AMHP would need to undertake a fresh MHA assessment with two Doctors and re-admit the patient, if justified.
However, if you re-imagine our exam question slightly: what happens if the patient absconded on day 24 and was then re-detained by the police or returned to hospital of their own accord on day 27? — does this change things? YES – because s21(2)(a) would apply and the “relevant time” is seven days after the person is returned to hospital and this gives the staff there sufficient time to further consider whether, for example, to apply for detention under s3 MHA by conducting the assessment they were about to do before the patient absconded. But all of that is a matter for the hospital to worry about once the patient is returned, not the police or others detaining.
The officers need only worry about whether the power under s18 MHA can still be used.
SECTION THREE
This thing also kicks in for s3 MHA and some other categories of patient who are near the end of their detention period, but they’re with a difference – again, it’s a difference for hospitals to worry about because anyone re-detaining an AWOL patient need only worry about whether s18 MHA offers a power to re-detain. Imagine our original exam question, but where the patient was a s3 MHA patient who absconded before the end of their six-month period of admission. Unlike s2 and some other, short-term provisions (see below), someone who absconds from s3 may be retaken for up to six months after they abscond, even where that date is after the day on which their six-month s3 admission would have ended.
Section 18(4) —
“A patient shall not be taken into custody under this section after the later of—
(a)the end of the period of six months beginning with the first day of his absence without leave; and
(b)the end of the period for which (apart from section 21 below) he is liable to be detained.”
So even if someone’s s3 MHA detention were due to expire on 9th September 2023, if they absented themselves on 4th September, they remain able to be re-detained under s18 MHA until 4th March 2024. If someone detains them before that date or if they return of their own volition, the hospital has the seven day period specified in s21 MHA to further assess them. If they are not found until 10th March, then we’re back to the police use of s136 or an AMHP conducting a new MHA assessment.
REMEMBER: the officers / others need only worry about whether the power under s18 MHA can still be used.
WE MIGHT AS DO WELL THE REST
There are some other legal situations which work in roughly the same way as for section 2 and s3 patients —
- Sections 4, 5(2) and 5(4) MHA — these are short-term orders for detention and you can look up what they mean elsewhere on the blog. Section 18 MHA works like it does for s2 MHA – once the original period of detention is up, you cannot use s18 MHA to re-detain someone who absented themselves whilst detained.
- Section 37 patients (hospital orders without a restriction order under s41 MHA) — in many respects treated like s3 MHA patients and for the purposes of this post, they are the same. A s37 patient will have a six month or twelve month detention period running and they are treated “as if” they were a s3 MHA patient for the purposes of AWOL / s18 MHA.
- All other categories of patient — s21 doesn’t matter at all because those patients never cease to be liable to be detained or because s18 MHA isn’t the power by which they’re redetained. You can read more about that in one of the Quick Guides.
There is also a Quick Guide to all the re-detention timescales for all patients.
FORGET ABOUT SECTION 21! – officers / others need only worry about whether the power under s18 MHA can still be used.
Winner of the President’s Medal,
the Royal College of Psychiatrists.
Winner of the Mind Digital Media Award

All opinions expressed are my own – they do not represent the views of any organisation.
(c) Michael Brown, 2023
I try to keep this blog up to date, but inevitably over time, amendments to the law as well as court rulings and other findings from inquests and complaints processes mean it is difficult to ensure all the articles and pages remain current. Please ensure you check all legal issues in particular and take appropriate professional advice where necessary.
Government legislation website – www.legislation.gov.uk