Can a patient under section 2 or 3 be arrested. << Yes.
I am aware a patient can be criminally prosecuted for a offence committed on section if they had criminal capacity at time of offence. << “Capacity” isn’t a concept in criminal law - a patient can be prosecuted even if they lack what is often referred to as capacity, for example if the offence is serious enough. The law presumes that everyone is sane and able to be held criminally responsible, unless / until the contrary is proved in court, for example by putting forward a defence of insanity.
But for example if the police were called for a loss of control incident on a ward and the officer diced to arrest a patient for say ‘criminal damage.’ << Perfectly legal of them to choose to do so, in principle. Of course whether they choose to do so is a different and much more complicated question. See below.
Could the police officer remove them from the ward and take them to a police station. << Could they? - yes. Should they? - see below.
Would section 17 leave be needed? << Depends - whilst safely under arrest at a police station, it isn’t strictly speaking required because the patient may be returned by the police after being detained in custody and / or questioned / charged, etc… But the s17 question is distinct from the criminal process so nothing prevents it being done, OR indeed the RC deciding to discharge the section entirely, which has happened. That has sometimes occurred because the hospital has determined that the circumstances giving rise to arrest mean it would be unsafe to have the patient back. This is why discussion is vital, to think about the post-police station practicalities, before we start removing hospitalised people to custody.
If not how can a nurse legally physical let the patient off the ward without making them AWOL? << It’s not a question of the nurse ‘letting’ this happen. Someone under arrest for an offence means the police have the right to do this, regardless of what the medical or nursing staff say, obviously subject to normal arrest rules about necessity and proportionality.
If section 17 was needed and a RC refused to write it up would they be committing an offence of Obstructing a Police Officer under section 89(2) Police Act 1996? << It wouldn’t be obstruction to fail to consider s17 leave because that’s nothing to do with the police and the arrest / removal can happen anyway. Obstruction would only occur if, for example, the doctor or nurses said they were refusing to let the patient be removed and / or keeping doors locked, etc… But I would like to think before removal was occurring or being contemplated, there had been a good, detailed discussion between the professionals about the allegation, the practicalities of different ways of proceeding and what will happen both at the police station and afterwards. Done properly, this should prevent the emergence of conflict about things like obstruction.
If the RC did refuse could a nurse still let PC and P out? - if not would nurse be committing the above. << Potentailly, yes - refuse to let the police officers leave when they say they’re leaving and you commit false imprisonment and refuse to allow an arrested person to go with them under arrest and you commit obstruction or resistance of a constable, at least in principle. Criminal law wins conflicts of laws.
If yes what would legally happen if RC refused s17 and patient couldn’t be let out ? And practically what is the officer meant to do? << If I knew of that happening and it couldn’t be resolved by clear discussion, I’d ask officers to record an offence of obstruction and initiative an investigation, during which I’d refer the incident to NHS managers and / or a regulator, as appropriate. Nobody has the right, in law, to obstruct the police when making lawful arrests. But as I say, good discussion about all of this is key to preventing the dispute in the first place.
Arresting someone who is hospitalised should be pretty much a last resort - most criminal investigations can occur without arrest, especially if someone is detained MHA.
Arrests should be justified on criminal law grounds only - ie, for the restoration of safety that cannot be otherwise guaranteed, search / seizure of property which can only be done after arrest, compulsory questioning of the suspect about their alleged involvement in an offence.
So the gravity of the allegation needs considering alongside those factors in point 2 - why would we seek the arrest of an acute ill, recently admitted psychotic patient for pushing someone or causing minor damage, for example? It would be highly likely they’d be considered unfit for detention in custody, unfit for questioning so what would be the legal basis for the arrest? However, if a patient on the verge of discharge who has had plenty of unproblematic s17 leave over recent weeks, punches a nurse fracturing their eye socket, it may well be justified.
Discussion - discussion - discussion - between the police, victim and professional staff. What are we attempting to achieve by immediate arrest, can it be done in a less restrictive way (that principle applies in criminal law as well as in the MHA) and what will happen in terms of the MHA once the person has been removed and detained.
What we must avoid at ALL costs - and I mention this because I’ve known it many times - is the police arresting someone when it’s not really necessary, only for the hospital to discharge the MHA completely and argue they cannot have someone back, only for the arrest process to require ongoing investigation or bail, etc., and then we have the recently ‘unsectioned’ patient in a police station car park with nowhere to go. If there is a management issue connected to a need for greater therapeutic security (for example, move to a PICU or MSU), that’s an internal matter for the NHS, not a criminal law matter for the police. Equally, the police should not be failing to take legitimate steps to investigate and crime and, if necessary, to arrest those suspects who require it for legal reasons (and those reasons are about the investigation of the offence and potential to prosecute - nothing more).
That’s why - at least for me - arrest is a last resort and something to be avoided wherever possible.
Hope this helps.