Medical Treatment: Decisions and the Law

2. Consent – Adults

Definition of capacity and its assessment

The person consenting must have the relevant mental capacity to do so

Capacity for those 16 years or over is to be determined by reference to the principles set out in the MCA. The MCA and the accompanying Code of Practice (which must be taken into account by those assessing capacity and caring for someone who lacks capacity), emphasise the need to involve and assist patients and those close to them in the decision-making process with regard to medical treatment. The MCA codifies and expands upon pre- existing common law principles in respect of the determination of capacity and provides a framework for decision-making for those who lack capacity in respect of medical treatment.

Although the test for determining capacity is now enshrined in s 3 of the MCA, there is no relevant distinction between the test as set out in the MCA and the previous common law test approved by the Court of Appeal in Re MB (an adult: medical treatment). As much of the MCA draws upon the existing common law principles, the pre-2007 jurisprudence remains relevant to determination of matters under the MCA.

The MCA makes clear that a person can only lack capacity because of an impairment or disturbance of mental or brain function. Refusal of treatment because of obstinance or belligerence will not suffice. As stated in s 2(1) and
(2) MCA, a person lacks capacity in relation to a matter if at the material time:

  • the person is unable to make a decision for himself (sometimes referred to as the ‘functional’ test); and
  • the inability to make a decision is because of a temporary or permanent impairment of or disturbance in the functioning of the person’s mind or brain (the ‘diagnostic’ test).Some examples of an impairment or disturbance in the functioning of the brain are given in paragraph 4.12 of the Code of Practice and include mental illness, dementia, organic brain injury, significant learning disabilities and intoxication.However, a finding of mental impairment and nothing more is not sufficient. The assessment of capacity must carefully consider each of the elements in s 2(1), applying the test in s 3(1):
  • Is there an impairment of or disturbance of the functioning of the mind or brain?
  • Is P ‘unable to make a decision for himself in relation to the matter’?
  • If so, what is the cause of that inability to make the relevant decision?A person will only lack capacity if there is a clear causative link between the inability to make the specific decision under consideration and the impairment of and disturbance in the functioning of the mind or brain. In PC & NC v City of York Council McFarlane LJ stated:

‘… There is, however, a danger in structuring the decision by looking to s 2(1) primarily as requiring a finding of mental impairment and nothing more and in considering s 2(1) first before then going on to look at s 3(1) as requiring a finding of inability to make a decision. The danger is that the strength of the causative nexus between mental impairment and inability to decide is watered down. That sequence – “mental impairment” and then “inability to make a decision” – is the reverse of that in s 2(1) – “unable to make a decision … because of an impairment of, or a disturbance in the functioning of, the mind or brain”. The danger in using s 2(1) simply to collect the mental health element is that the key words “because of” in s 2(1) may lose their prominence and be replaced by words such as those deployed by Hedley J: “referable to” or “significantly relates to”.’

The phrase ‘at the material time’ in s 2(1) is also of importance: capacity must be considered at the time the relevant decision is to be made. As capacity is decision-specific, it must also be considered in the context of the specific decision that has to be made.

The statutory test for capacity is found in s 3 MCA which provides that:

‘(1)… a person is unable to make a decision for himself if he is unable –
(a) to understand the information relevant to the decision,
(b) to retain that information,
(c) to use or weigh that information as part of the process of making the decision, or
(d) to communicate his decision (whether by talking, using sign language or any other means).’

Any question of capacity falls to be determined on the balance of probabilities.
Discrimination must be avoided – lack of capacity cannot be established by reference to:
(a) a person’s age or appearance; or
(b) a condition of his, or an aspect of his behaviour, which might lead others to make unjustified assumptions about his capacity.


  • A Adult  2.1
  • B Capacity  2.2
  • Definition of capacity and its assessment 2.2
    • The person consenting must have the relevant mental capacity to do so 2.2
    • How much capacity? 2.6
  • Temporary incapacity 2.7
  • Presumption of capacity  2.8
  • The absolute nature of an adult’s consent 2.9
  • Treatment must be lawful 2.10
  • C Refusal 2.11
  • D Change of mind  2.12
  • E Advance decisions 2.13
  • General principle  2.13
  • Requirements  2.14
    • Validity  2.15
    • Applicability  2.16
  • Form  2.17
  • Informed refusal?  2.18
  • Knowledge  2.19
  • Duration  2.20
  • Records  2.21
  • F Conclusion  2.22
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