The Mental Health Act ([179]) is concerned with the treatment of a person's mental disorder, while the Mental Capacity Act ([176]) has a broader scope that includes physical and mental health as well as welfare, finances, property and research participation.

Someone who is deemed to have a mental disorder may or may not have capacity, and someone who does not have capacity may or may not have a diagnosis of a mental disorder. It is entirely possible for someone assessed and detained under the Mental Health Act to have capacity in relation to a treatment decision. Whether an individual patient has or does not have decision‐making capacity is not the key determinant of whether the Mental Health Act should be used. If a patient were already detained and subject to the compulsory treatment provisions of the Mental Health Act, the Mental Capacity Act would not be used for the provision of further medical treatment for that mental disorder; thus, best interests principles would not apply in the same way. However, it would still be possible to apply the Mental Capacity Act for other aspects of care if the patient lacked capacity for related decisions. Based on the specific case and needs of a patient with a ‘mental disorder’, staff must decide which act and subsequent approaches is least restrictive to the individual (Browne Jacobson LLP [38]). Both the Mental Capacity Act and the Mental Health Act provide procedural safeguards to ensure the rights of the person concerned are protected during their detention, and staff need to consider which safeguards will best protect the interest of the patient (Table 5.25).

The interested reader may want to visit www.brownejacobson.com, www.39essex.com or www.no5.com for accessible summaries of the relevant legislation and case law.