15.2 Consent, Capacity & the Mental Capacity Act 2005
Key Takeaways
Valid consent requires voluntary agreement, comprehensive information disclosure, and decision-making capacity; the Montgomery v Lanarkshire (2015) ruling established that clinicians must disclose all material risks that a reasonable patient in that individual's position would consider significant.
The Mental Capacity Act 2005 (MCA) rests on five statutory principles: presumption of capacity, support to make decisions, right to make unwise decisions, best interests, and the least restrictive intervention.
Capacity assessment is a two-stage functional test (diagnostic impairment of mind/brain plus functional inability to understand, retain, weigh, or communicate the decision) and is strictly decision-specific and time-specific.
An Advance Decision to Refuse Treatment (ADRT) refusing life-sustaining therapy is legally binding only if it is valid, applicable, written, signed, witnessed, and explicitly states 'even if life is at risk'.
Children under 16 can consent to medical treatment if they satisfy Gillick competence; Fraser guidelines specifically govern confidential sexual health advice and contraception, though a minor's refusal of life-saving care can be overridden by parental responsibility or the High Court.
Consent, Capacity & the Mental Capacity Act 2005
Consent is the fundamental ethical and legal mechanism through which patient autonomy is respected in modern clinical practice, codified in GMC guidance (Decision making and consent). Touching a patient without valid consent constitutes battery in civil law and assault in criminal law. In England and Wales, clinical decision-making for patients who may lack decision-making capacity is governed by the Mental Capacity Act 2005 (MCA).
Principles of Valid Consent & The Montgomery Ruling
For consent to be legally and ethically valid, three essential criteria must be satisfied:
- Voluntary: The decision must be made freely by the patient, entirely free from coercion, undue influence, or pressure by healthcare staff, family members, or carers.
- Informed: The patient must receive adequate, comprehensible information regarding the proposed procedure, its anticipated benefits, potential risks, reasonable alternatives (including conservative management or doing nothing), and the consequences of refusal.
- Capacitous: The patient must have the mental capacity to make the specific decision at the time it is required.
The Landmark Montgomery v Lanarkshire Ruling (2015)
Historically, the adequacy of risk disclosure was determined by the Bolam test (whether the doctor acted in accordance with a responsible body of medical opinion). The UK Supreme Court's landmark decision in Montgomery v Lanarkshire Health Board [2015] rejected this paternalistic model, establishing that consent must be patient-centered.
Important
The Montgomery Standard of Material Risk: Doctors have a legal duty to disclose any material risk. A risk is defined as material if:
- A reasonable person in the patient's position would be likely to attach significance to it, OR
- The doctor is, or should reasonably be, aware that the particular patient would be likely to attach significance to it.
Risk disclosure cannot be reduced to a mechanical checklist of percentages; it requires an active dialogue exploring what matters specifically to the individual patient (e.g., a 1% risk of hand tremor may be negligible to an office worker, but catastrophic to a professional concert violinist).
The Mental Capacity Act 2005: Five Statutory Principles
The Mental Capacity Act 2005 (MCA) provides a comprehensive legal framework for individuals aged 16 and older in England and Wales who lack the capacity to make decisions for themselves:
| Principle | Legal Definition | Clinical Implications |
|---|---|---|
| 1. Presumption of Capacity | A person must be assumed to have capacity unless it is established that they lack capacity. | Clinicians cannot assume lack of capacity based solely on age, appearance, medical diagnosis (e.g., dementia, schizophrenia), or cognitive impairment. |
| 2. Support to Make Decisions | A person is not to be treated as unable to make a decision unless all practicable steps to help them have been taken without success. | Provide information using tailored communication aids, visual diagrams, interpreters, hearing aids, or choosing optimal times of day when cognition is sharpest. |
| 3. Right to Make Unwise Decisions | A person is not to be treated as lacking capacity merely because they make an unwise or eccentric decision. | A competent adult has the legal right to refuse life-saving treatment (e.g., refusing blood transfusion or amputation), even if clinicians consider the choice irrational or fatal. |
| 4. Best Interests | Any act done or decision made under the MCA for or on behalf of a person who lacks capacity must be done in their best interests. | Clinicians must apply a structured checklist considering the person's past and present wishes, values, beliefs, and consultation with loved ones. |
| 5. Least Restrictive Option | Before making a decision, consider whether the purpose can be effectively achieved in a way that is less restrictive of the person's rights and freedom. | Choose medical interventions that preserve independence and autonomy while avoiding unnecessary chemical or physical restraint. |
The Two-Stage Functional Test of Capacity
Mental capacity is decision-specific (a patient may have capacity to choose their daily diet, but lack capacity to consent to complex neurosurgery) and time-specific (capacity can fluctuate with acute delirium, intoxication, or dementia progression).
The Four Functional Elements (Stage 2)
- Understand: Comprehend the nature, purpose, benefits, risks, and alternatives of the decision, including the consequences of doing nothing.
- Retain: Hold the information in memory long enough to process and arrive at a decision (short-term retention is sufficient).
- Weigh Up: Balance the risks and benefits against personal values to reach an outcome.
- Communicate: Express the decision through verbal speech, writing, sign language, or non-verbal gestures (e.g., blinking, squeezing a hand).
Best Interests Decision-Making & Legal Instruments
When a patient is determined to lack capacity for a specific medical decision, healthcare professionals must act in their best interests under Section 4 of the MCA.
The Best Interests Balance Sheet
Clinicians must not make decisions based merely on what they consider medically optimal. They must consult the following:
- Past and Present Wishes: Review advance statements, personal diaries, and previously expressed verbal wishes or religious beliefs.
- Consultation with Loved Ones: Consult family members, partners, carers, and friends to ascertain what the patient would have wanted.
- Independent Mental Capacity Advocate (IMCA): An IMCA is an independent statutory advocate who must be instructed when an individual lacks capacity, is unbefriended (has no family, partner, or unpaid carer to represent them), and faces decisions regarding serious medical treatment (e.g., major surgery, chemotherapy, PEG tube insertion) or long-term accommodation moves (>28 days in hospital or >8 weeks in a care home).
Lasting Power of Attorney (LPA)
A competent adult (the donor) can appoint an attorney to make decisions on their behalf should they lose capacity:
- LPA for Health and Welfare: Applies strictly when the patient lacks capacity. It must be formally registered with the Office of the Public Guardian (OPG) before use.
- Life-Sustaining Treatment Clause: The LPA attorney only has legal authority to consent to or refuse life-sustaining treatment if the donor explicitly ticked and signed the specific section granting that power in the registered document.
Advance Decision to Refuse Treatment (ADRT)
An ADRT (formerly known as an advance directive or "living will") allows a competent individual aged 18 or older to refuse specified future medical treatments for a time when they may lack capacity.
Caution
Strict Legal Criteria for ADRTs Refusing Life-Sustaining Care: If an ADRT refuses life-sustaining treatment (e.g., mechanical ventilation, cardiopulmonary resuscitation, artificial nutrition/hydration), it is legally binding on clinicians only if it satisfies all of the following statutory criteria:
- It must be in writing.
- It must be signed by the patient (or by someone in their presence and at their direction).
- It must be witnessed and signed by an independent witness.
- It must contain the explicit, clear statement: "even if life is at risk".
If valid and applicable to the current clinical circumstances, a compliant ADRT carries the same legal weight as a contemporaneous refusal by a competent adult and overrides clinical best-interests assessments.
Minors, Gillick Competence & The Fraser Guidelines
Young People Aged 16 and 17
Under Section 8 of the Family Law Reform Act 1969, adolescents aged 16 and 17 are presumed in law to have capacity to consent to their own surgical, medical, or dental treatment without parental involvement.
Gillick Competence (Children Under 16)
Originating from Gillick v West Norfolk and Wisbech AHA [1985], a child under 16 has legal capacity to consent to medical examination and treatment if they demonstrate sufficient understanding and intelligence to fully comprehend what is proposed, its risks, benefits, and long-term implications.
The Fraser Guidelines (Contraception & Sexual Health)
Lord Fraser established five specific guidelines governing when a doctor may provide contraception, abortion advice, or sexual health treatment to a young person under 16 without parental knowledge or consent:
- The young person understands the doctor's clinical advice.
- The doctor cannot persuade the young person to inform their parents, nor will they permit the doctor to inform them.
- The young person is very likely to begin or continue having sexual intercourse with or without contraceptive treatment.
- Unless the young person receives contraceptive treatment or advice, their physical or mental health (or both) is likely to suffer.
- The young person's best interests require the doctor to provide contraceptive advice and/or treatment without parental involvement.
Refusal of Treatment by Minors
A fundamental legal asymmetry exists regarding refusal of treatment:
- Competent Adults (≥18): A competent adult's refusal of medical intervention is absolute and legally binding, even if it leads to death.
- Minors (Under 18): If a Gillick-competent child (<16) or a 16–17 year old refuses life-saving treatment (e.g., refusing blood transfusion or chemotherapy), their refusal is not absolute. Under English law (Re W [1992], Re R [1991]), a refusal by a minor can be legally overridden by someone holding Parental Responsibility or by the High Court exercising its inherent jurisdiction, if overriding the refusal is deemed to be in the child's overriding best interests.
A 74-year-old woman with a history of moderate vascular dementia is admitted to the surgical ward with acute cholecystitis. The surgical consultant recommends an urgent laparoscopic cholecystectomy to prevent perforation. The doctor explains the procedure, benefits, risks (including conversion to open surgery and bile duct injury), and conservative treatment options using clear language and visual diagrams. When assessed, the patient understands the disease, recognizes the risks of surgery versus antibiotics, retains the information, and explains: 'I am 74 years old and I refuse to undergo surgery. I accept the risk of infection returning and I choose conservative antibiotic treatment.' Her son, who has no formal legal powers, demands that the surgical team proceed with surgery immediately, claiming his mother's dementia invalidates her refusal. What is the most appropriate course of action?
Proceed with laparoscopic cholecystectomy based on the son's proxy consent as next of kin
Deem the patient to lack capacity because refusing definitive surgery for acute cholecystitis is an irrational medical decision
Respect the patient's refusal of surgery because she demonstrates decision-making capacity and has the legal right to make an unwise decision
Refer the case urgently to the Court of Protection to obtain a mandatory surgical authorization order
A 48-year-old man who is a devout Jehovah's Witness is brought to the emergency department following an industrial crush injury. He has sustained severe pelvic fractures with massive retroperitoneal haemorrhage. His haemoglobin is 38 g/L and he is in refractory haemorrhagic shock. The patient is currently intubated, sedated, and ventilated. His sister arrives and presents a signed, witnessed Advance Decision to Refuse Treatment (ADRT) document created 6 months earlier when he was fully competent. The typed document explicitly states: 'In the event of illness or trauma, I refuse the administration of all allogeneic blood products under any circumstances, even if my life is at risk.' The trauma team leader considers whether to administer emergency O-negative blood products to prevent cardiac arrest. What is the most appropriate clinical decision?
Withhold all allogeneic blood transfusions and continue aggressive non-blood volume resuscitation and urgent surgical or interventional radiological haemostasis
Override the advance directive because the Mental Capacity Act does not permit individuals to refuse life-sustaining treatment in emergency trauma situations
Request the sister to sign a formal hospital indemnity waiver overriding the advance decision so blood can be transfused
Administer emergency blood transfusion immediately under the doctrine of emergency best interests because life preservation takes precedence over written advance directives
A 15-year-old girl attends an appointments-only general practice clinic requesting the administration of a progestogen-only contraceptive implant (Nexplanon). During a private consultation, she demonstrates a mature grasp of how the implant works, its potential side effects (such as irregular bleeding), and the ongoing need for barrier contraception to prevent sexually transmitted infections. She states that she has been in a relationship with her 16-year-old boyfriend for six months. She adamantly refuses to discuss this with her parents, fearing that their religious beliefs will result in her being removed from school. What is the most appropriate clinical action?
Make an immediate emergency referral to local child safeguarding social services due to unlawful sexual activity in a minor
Provide confidential contraceptive counseling and insert the implant under the Fraser guidelines without notifying her parents
Refuse to insert the contraceptive implant until she brings a parent or legal guardian to give formal written consent
Agree to insert the implant on the condition that the practice writes an explanatory letter to her parents following the procedure
Sections you finish are checked off in the contents.