On the issue of training for the police in regards to mental health, there’s been an interesting recent review on the broader issue from a police perspective by Her Majesty’s Inspectorate of Constabulary and Fire & Rescue Services (the body responsible for reporting on the efficiency and effectiveness of police forces in England and Wales).
Policing and Mental Health (November 2018) reflects on the increasing degree to which the police are responding to people living with mental health problems in variety of situations. It noted that while forces are investing in training, the quality of this remains inconsistent across England and Wales, stating:
Only around a third of forces have invested heavily in mental health training (in terms of time allocated in the training calendar and the breadth of different areas of mental health the training covers).
Many forces are too reliant on e-learning with less opportunities for face-to-face, instructor-led discussions to cover more complex topics.
The report also found ‘a general lack of understanding by forces of the extent and nature of their mental health demand’ and emphasised the need for more collaborative work with partner organisations to gain a clear picture and help plan out their approach.
Some of these findings do seem to ring true with the specific example cited here. Whether the officers should have been put in a position of needing to care for the people involved for several hours is obviously a question, but it appears as though there certainly isn't the capacity to do this, nor the appropriate training.
In terms of security staff, again there is a question of whether we should be reaching a situation where they are responsible for caring for people living with mental health problems for extended periods of time in these circumstances, but either way it would seem sensible that those working in health care settings do undertake appropriate training in this respect.
The National Association for Healthcare Security act as a professional body for security staff in the NHS, though I don't believe membership is mandatory for those carrying out these roles in the NHS, maybe this is an issue they are aware of and could help to take this forward.