This Act is currently undergoing revision in Parliament, and some revisions have caused controversy, dealing as they do with a small fraction of the population who have severe personality disorder that may predispose them to be a danger to the public but who do not have a diagnosed mental illness presently. However these changes are unlikely to affect the vast majority of people who come into contact with mental health services.

The Mental Health Act (MHA), in a nutshell, attempts to define ‘mental impairment’ or ‘psychopathic disorder’ in a legal rather than medical way as an illness which “is associated with abnormally aggressive or seriously irresponsible conduct on the part of the person concerned”. However it does not define ‘mental illness’ per se, even though people do not have to have legally-defined ‘mental impairment’ to be detained under the MHA.

The Department of Health has attempted a definition of ‘mental illness’ that is not as such enshrined in law but may be used by practitioners working under the Mental Health Act. It must include one or more of the following features:

• More than temporary impairment of intellectual functions shown by a failure of memory, orientation, comprehension or learning capacity.
• More than temporary alteration of mood of such degree as to give rise to the patient having a delusional appraisal of his situation, his past or his future, or that of others or to the lack of any appraisal.
• Delusional beliefs, persecutory, jealous or grandiose.
• Abnormal perceptions associated with delusional misinterpretation of events.
• Thinking so disordered as to prevent the patient making a reasonable appraisal of his situation or having reasonable communication with others.

Importantly, the MHA states very clearly that people must not be deemed to have a form of Mental Disorder "by reason only of promiscuity or other immoral conduct, sexual deviancy or dependence on alcohol or drugs".

The MHA empowers certain professionals to detain people who are considered to be a danger to themselves or the public and fit one of the above definitions. This is known familiarly as being ‘sectioned’.

Sections 2 and 3 require two professionals (usually a psychiatrist and a social worker qualified under the Act) to authorise detention for, respectively, up to 28 days (non-renewable) for assessment and six months (renewable) for treatment.

Section 4, which is quite rarely used, allows a single medical professional to detain a person in an emergency situation for up to 72 hours.

Section 5 allows a doctor or nurse to prevent someone who is already in hospital on a voluntary basis from discharging themselves for up to 72 hours.

Sections 135 and 136 allow a police officer to take someone from a public place or from their home to a ‘place of safety’ (usually meaning a hospital) where they can be assessed. This is not a ‘section’ as such.

Other sections allow for particular types of detention ordered by courts in criminal cases.

Sectioning is not a course of action undertaken lightly by professionals and every effort will be made to get the person to agree to a voluntary admission unless they are incapable of doing so. A person’s discharge from detention is usually ordered by the responsible professional (usually the psychiatrist) or, in the case of dispute, by a mental health tribunal, but can be requested with 72 hours’ notice by the next of kin – though this can be blocked by the responsible medical officer.

Other sections of the Act specifically cover consent to treatment, and a whole different set of legislation – the law on Capacity – also comes into play to cover situations where the person may or may not have a diagnosed mental illness but may be incapable of understanding why they need treatment or giving informed consent to it. Capacity applies to situations where people are both physically and/or mentally incapacitated.

Further reading on the Mental Health Act

A good general guide to the Mental Health Act 1983 is at http://www.hyperguide.co.uk/mha/