UK: The Legal Test for Mental Capacity

Last Updated: 2 September 2010
Article by Suzanne Marriott

What is Mental Capacity?

In the legal context mental capacity is the ability to make decisions. Examples of the situations in which it might be particularly important to establish a person's mental capacity include when in relation to making a will, undertaking lifetime giving or making a lasting power of attorney. Establishing mental capacity (or incapacity) might also be particularly important in relation to decisions about an individual's physical well-being, including about the medical treatment he/she is to receive. It might also be relevant in relation to more humdrum decisions about an individual's everyday activities and lifestyle. The test of mental capacity here is a legal test rather than a medical test or diagnosis. And what is important in assessing mental capacity is to focus on the processes by which a decision is made, rather than on the decision itself.

What is the Legal Test for Mental Capacity?

The Mental Capacity Act 2005 ("MCA") which came into force on I October 2007 creates a statutory test for capacity. This test applies for the purposes of the Act. Situations covered by the Act in which the statutory test is therefore relevant include the determination whether an individual has capacity to enter into an advance decision (by which such person sets out the circumstances in which they would not want to receive medical treatment in the event of loss of capacity) or to enter into a lasting power of attorney. It is also relevant to the appointment of a so-called independent mental capacity advocate and to the Court of Protection's power to make orders in the event that a person lacks capacity. Under this statutory test anyone claiming that a person lacks capacity must be able to show on a balance of probabilities (that is, there is a more than 50% likelihood) that this is the case.

The MCA 2005 provides that a person lacks capacity in relation to a matter if he/she is unable to make a decision for him/herself in relation to the matter because of an impairment of or disturbance in the functioning of the mind or brain. This is therefore a two-stage test. First it is necessary to ask "Does the person have an impairment of, or a disturbance in the functioning of their mind or brain?" Such impairment or disturbance may be permanent or temporary. It might be caused, for example, by significant learning disabilities, physical medical conditions that cause confusion, loss of consciousness, delirium, the symptoms of alcohol or drug abuse or dementia.

The second part of the test for capacity asks the question whether the impairment or disturbance means that the person in question is unable to make a specific decision when they need to. The Act provides that a person is unable to make a decision for him/herself if he/she is unable:

  • to understand the information relevant to the decision (including information about the reasonably foreseeable consequences of deciding one way or the other or of failing to make a decision – and for this purpose, information can be provided to him in a simplified form);
  • to retain that information (although it is acceptable if the person can retain the information only for a short time);
  • to use the information as part of the decision-making process; or
  • to communicate his decision by any means, including sign language.

The Act lays down some important principles or safeguards in relation to determining capacity.

  • A person must be assumed to have capacity unless it is established that he/she lacks it.
  • A person 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. This might mean making sure that the person is in a suitable and comfortable environment or it might mean involving an expert in helping the person to express his/her views.
  • A person is not to be treated as unable to make a decision merely because he/she makes an unwise decision.

Furthermore, lack of capacity cannot be established simply by reference to a person's age or appearance or an aspect of behaviour which might lead others to make unjustified assumptions about capacity.

The legal test of mental capacity is one of a person's ability to make a particular decision at a particular point in time, rather than of his ability to make decisions generally. For example, a person may have capacity to pay bills but lack the capacity to manage investments. Furthermore, a person's capacity may fluctuate such that they lose and regain capacity, perhaps dependent on their condition from day to day or within a single day.

Case-Law Tests for Mental Capacity

As mentioned above, the test for mental capacity set out in the MCA 2005 is expressed to apply "for the purposes of this Act". There are other legal tests of mental capacity for different situations such as making a will, entering into contracts and embarking on litigation. These tests are mainly set out in case-law. Where case-law provides a test of capacity in a particular context it will be necessary to have regard to this as well as to the MCA 2005. For example, in accordance with the case-law test of capacity for making or revoking a will the testator or testatrix in broad terms must be able to:

  • understand the nature of the act of making a will and its effects; and
  • understand the extent (as distinct from the value) of the property of which he or she is disposing; and
  • comprehend and appreciate the claims to which he or she ought to give effect.

Furthermore, a person making a will should have testamentary capacity at two stages:

  • when he or she gives instructions for preparation of the will; and
  • when the will is executed.

If the testator becomes ill between giving instructions and executing the will, then provided the will exactly reflects the instructions given then the testator may not need capacity (as specified above) at execution.

In practice, as cases on capacity come before the courts, the multiple legal tests for capacity in different situations may gradually become subsumed under the test set out in the MCA 2005 which is in any event broadly in line with the case-law tests. For the time being however, regard must be had to the separate but overlapping tests where these are applicable.

Who Appraises an Individual's Mental Capacity?

Different people may be involved in assessing the person's capacity depending upon the particular decision being made. Importantly the person assessing capacity does not need to be an expert. For example, a family member or carer may decide whether a person has capacity to agree to their day to day routine. A doctor may assess whether a person consents to treatment whilst a solicitor may assess a person's capacity to make a will or enter into a lasting power of attorney. In some cases it may be necessary to obtain a professional opinion. This may be the case if, for example, the decision is a particularly significant or serious one, or if there is disagreement about the individual's capacity or someone is likely to challenge it.


In some cases determining whether an individual has capacity to make particular decisions can be very difficult. In cases of doubt, and particularly where decisions are very significant, for example in relation to medical procedures and/or where there are major financial implications, it is vital that care is taken to follow appropriate procedures to assess capacity. The Office of the Court of Protection ("OCP") has published a Code of Practice which includes guidance on this. The code of practice can be downloaded from the OPG's website at It may in some cases be helpful or advisable to obtain professional or expert legal and/or medical opinion, for example from a consultant who specialises in providing such appraisals.

In connection with this briefing, you might also like to see our two of our other briefing notes entitled "Making a Lasting Power of Attorney" and "Making an Advance Decision about Medical Treatment".

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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