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Capacity Assessments: when, what and how?

01 August 2023

Due to the myriad of recent case law, especially when attempting to navigate complicated health scenarios, these questions are difficult to answer. In this article we go back to basics to examine when to undertake a capacity assessment, how to do so and what this assessment should consist of. 


The core principles of the Mental Capacity Act ('MCA') 2005 are set out in s.1. They are:

  • s.1 (2): a person (P) must be assumed to have capacity unless it is established that he lacks capacity;
  • s.1 (3): P is not to be treated as unable to make a decision unless all practicable steps to help him to do so have been taken without success;
  • s.1 (4): P is not to be treated as unable to make a decision merely because he makes an unwise decision;
  • s.1 (5): an act done, or decision made, under this Act for or on behalf of a person who lacks capacity must be done, or made, in his best interests; and
  • s.1 (6): before the act is done, or the decision is made, regard must be had to whether the purpose for which it is needed can be as effectively achieved in a way that is less restrictive of the person’s rights and freedom of action.

That the person is, initially at least, presumed to have capacity is the fundamental principle from which all others flow.

Consequently, it is for the decision maker, not the patient, to prove that the patient does not have capacity to make a decision. The decision maker, the individual who considers it necessary to undertake a treatment decision on the patient's behalf, takes on the burden of determining the patient's capacity. 

The decision maker cannot delegate an assessment of capacity to another. So an orthopaedic surgeon who advises an amputation of the patient's lower limb, cannot delegate the capacity assessment to a psychiatrist. That does not mean assistance cannot be sought and sometimes it is vital to obtain expert help. Ultimately however, the treating doctor must reasonably believe the patient lacked capacity. 

So going back to our fictional orthopaedic surgeon, if the surgeon undertook the amputation and did not reasonably believe the patient lacked capacity, then the defence of 'the doctrine of necessity' pursuant to s5 of the MCA to a claim for a civil or criminal prosecution will not be open to the surgeon. 

What is a lack of capacity?

The MCA provides very clear guidance on what is meant by determining a patient has a lack of capacity. 

s2(1) of the MCA provides that:

‘a person lacks capacity in relation to a matter if at the material time he is unable to make a decision for himself in relation to the matter because of an impairment of, or a disturbance in the functioning of, the mind or the brain'

In the recent case of North Bristol NHS Trust v R [2023] EWCOP 5:

"the court was not precluded from reaching a conclusion on that question in the absence of a formal diagnosis or in the absence of the court being able to formulate precisely the underlying condition or conditions. The question for the court remained whether, on the evidence available to it, the inability to make a decision in relation to the matter was because of an impairment of, or a disturbance in the functioning of, the mind or brain,"

The MCA also clearly sets out the assessment required in order to determine whether a patient is able to make a decision. 

s3(1) states that Patient is unable to make a decision for himself if he is unable:

  • To understand the information relevant to the decision; or
  • To retain that information; or
  • To use or weigh that information as part of the process of making the decision; or
  • To communicate his decision (whether by talking, using sign language or any other means)

Fluctuating capacity 

There will be times where a patient's capacity to make a decision about their treatment fluctuates. If the treatment relates to a one off decision then it may be possible to defer making the decision until such time the patient regains capacity. 

Alternatively it may be possible to undertake minimal treatment until such time the patient is able to make such a decision. Of course if you have a patient that requires renal dialysis three times per week (and there are only limited periods during which the patient does have capacity), it may be appropriate to proceed on the basis the patient does not have capacity. 

If in doubt, this would certainly be an occasion to seek legal advice. 


Top tips when undertaking a capacity assessment  

  • Ensure you are clear about what decision you are asking the patient. Don’t over complicate the decision.
  • Document why you consider the patient lacks capacity.
  • What are the relevant points the patient needs to understand (they don’t need to understand every nuanced point).
  • Make sure you have clearly explained all of the options to a patient.
  • Be patient. Take the time to ensure that you have assisted the patient to make a decision – do you need to have a second conversation with the patient to enable them to reach a decision? 
  • Document your reasons as to why the patient is unable to understand, retain, weight up and balance and communicate the decision to the decision maker. 


It is important to remember that if the patient is deemed to have capacity, they are entitled to make an unwise decision. 

As stated by the Judge in the Heart of England NHS Trust v JB case" do not allow the tail of welfare to wag the dog of capacity".

Should you wish to discuss any of the issues raised in this insight, please contact the Police, Care and Justice team

Further Reading