23.3 Mental Capacity & UK Mental Health Law

5. Mental Capacity & Statutory UK Legal Framework

Medical practitioners must understand the statutory boundaries governing patient autonomy, consent, capacity, and compulsory psychiatric intervention under UK law.

Mental Capacity Act 2005 (England & Wales)

The Mental Capacity Act (MCA) 2005 governs decision-making on behalf of individuals aged 16 and older who lack decision-making capacity.

• Five Core Statutory Principles:
  1. Presumption of Capacity: Every individual is assumed to have capacity unless proven otherwise.
  2. Support to Make Decisions: A person cannot be treated as unable to make a decision unless all practicable steps to help them do so have failed.
  3. Right to Make Unwise Decisions: An eccentric, irrational, or unwise decision does not in itself establish a lack of capacity.
  4. Best Interests: Any act done or decision made on behalf of an incapacitated person must be in their best interests.
  5. Least Restrictive Alternative: Interventions must restrict the person's rights and freedom of action as little as possible.
• Two-Stage Functional Test of Capacity:
  • Capacity is strictly decision-specific and time-specific (a patient may have capacity to choose their lunch or consent to venepuncture, but lack capacity to consent to a complex surgical procedure or refuse life-saving dialysis).
  • Stage 1 (Diagnostic Threshold): Does the person have an impairment of, or a disturbance in the functioning of, the mind or brain (temporary or permanent, e.g. delirium, dementia, intoxication, head injury, acute psychosis)?
  • Stage 2 (Functional Assessment): Does that impairment render the person unable to perform ANY of the following four functional steps?
    1. Understand the information relevant to the decision (including benefits, risks, and consequences of refusing).
    2. Retain that information long enough to make the decision.
    3. Use or weigh that information as part of the process of making the decision.
    4. Communicate their decision (by speech, sign language, blinking, or any other means).
• Best Interests Determinations & Legal Proxies:
  • When a patient lacks capacity, clinicians make decisions under the MCA using a structured Best Interests checklist (considering the patient's past/present wishes, beliefs, values, and consulting family/carers).
  • Lasting Power of Attorney (LPA) for Health and Welfare: Legally appointed proxy who can make medical decisions only when the patient lacks capacity. Cannot override life-sustaining treatment unless specifically authorized in the registered LPA deed.
  • Advance Decision to Refuse Treatment (ADRT): Legally binding refusal of specific treatments. To apply to life-sustaining treatment, it must be in writing, signed, witnessed, and explicitly state "even if life is at risk". A valid and applicable ADRT overrides best interests decisions.
  • Independent Mental Capacity Advocate (IMCA): Statutory advocate required when an unbefriended patient lacking capacity faces serious medical treatment decisions or long-term care moves.
• Deprivation of Liberty Safeguards (DoLS) / Liberty Protection Safeguards (LPS):
  • Applied when an incapacitated adult is deprived of liberty in a hospital or care home.
  • Defined by the Supreme Court Cheshire West "Acid Test": The person is (1) subject to continuous supervision and control, AND (2) not free to leave, AND (3) lacks capacity to consent to those arrangements.

Mental Health Act 1983 (Amended 2007)

The Mental Health Act (MHA) provides statutory powers for the compulsory detention and treatment of individuals with a mental disorder who pose a significant risk to their own health, safety, or to others.

• Key Statutory Sections for the Medical Ward:
  • Section 2 (Assessment): Admission for assessment (and treatment) of mental disorder. Duration: Up to 28 days (cannot be extended or renewed). Requires recommendations from two medical practitioners (one of whom must be approved under Section 12, e.g. a consultant psychiatrist) plus an Approved Mental Health Professional (AMHP) or nearest relative.
  • Section 3 (Treatment): Admission for treatment of a confirmed mental disorder where appropriate medical treatment is available. Duration: Up to 6 months (renewable). Requires two medical practitioners (one Section 12 approved) plus an AMHP.
  • Section 4 (Emergency Admission): Emergency admission for assessment when Section 2 would cause unacceptable delay. Duration: Up to 72 hours. Requires one medical practitioner (preferably knowing the patient) and an AMHP. Converts to Section 2 upon second medical recommendation.
  • Section 5(2) (Doctor's Holding Power): Detains an informal inpatient already admitted to a hospital bed (medical, surgical, or psychiatric ward) who expresses intent to leave and meets detention criteria. Duration: Up to 72 hours (non-renewable). Completed by the registered medical practitioner in charge of the patient's treatment or their nominated deputy. Cannot be used in the Emergency Department (A&E is not an inpatient ward) or on outpatients.
  • Section 5(4) (Nurse's Holding Power): Applied by an authorized mental health or learning disability nurse to detain an informal inpatient up to 6 hours while awaiting a medical practitioner to complete Section 5(2).

CRITICAL LEGAL BOUNDARY: Physical vs Psychiatric Treatment

• A foundational MRCP Part 1 principle: The Mental Health Act CANNOT be used to enforce treatment for purely physical medical conditions (e.g. antibiotic therapy for sepsis, emergency laparotomy, percutaneous coronary intervention, insulin for DKA) against a competent patient's refusal, or on an incompetent patient whose physical illness is unrelated to their mental disorder.
• Single Exception: Physical treatment is permissible under the MHA only if it is directly treating, or is an integral physical consequence of, the mental disorder itself (e.g. nasogastric refeeding for life-threatening anorexia nervosa, or suturing a self-inflicted wound immediately following a psychotic act).
• Refusal of Physical Treatment: If an inpatient refuses physical medical care:
  1. Assess decision-specific capacity under the Mental Capacity Act 2005.
  2. If the patient has capacity → their refusal must be respected, even if it results in death.
  3. If the patient lacks capacity (e.g. due to delirium, dementia, or severe psychosis impairing ability to weigh physical risk) → provide necessary physical medical treatment in their Best Interests under the Mental Capacity Act 2005, using the least restrictive means.