The law and mental capacity

Definition and tests

A deafblind person walking along and holding another's hand 'Mental capacity' means a person's ability to make their own choices and decisions.

Under UK law, someone’s capacity is judged according to the specific decision to be made, so a person may have sufficient capacity to make simple decisions but not more complicated ones.

In England and Wales the Mental Capacity Act says that a person lacks capacity to make a decision if they have an ‘impairment of or disturbance in the function of their mind or brain’ (either temporary or permanent), and as a result they cannot do one or more of the following:

  • Understand the information relating to this particular decision (including its benefits and risks)
  • Retain the information for long enough to make this decision
  • Weigh up the information involved in making this decision
  • Communicate their decision in any way.

If in doubt, you must assume the person does have capacity (see below).

Northern Ireland uses a slightly different 'common law' test, but the result will usually be the same.

Who checks capacity?

Capacity should be checked by whoever wants the particular decision to be taken. If the issue is around medical treatment, this will be done by a doctor. However, for routine decisions it will often be a carer or family member who decides whether the person is capable of making their own decision.

Principles of mental capacity law

  1. You must assume that the person does have capacity to make their own decision unless there is clear evidence that they do not
  2. You must take all practicable or reasonable steps to help the person make their own decision before you conclude that they lack capacity to do so
  3. The fact that someone has made an unwise decision does not, in itself, mean that they lack capacity. We all make mistakes
  4. Anything you do on behalf of someone who lacks capacity must be in their best interests
  5. Consider whether you can achieve the same result in a less restrictive way

Best interests

These are not defined in law. However, the Mental Capacity Act in England and Wales lists some factors you must take into account when deciding what is in someone’s best interests. These include:

  • Considering whether the decision can wait until the person regains capacity
  • Involving the incapacitated person in the decision-making if possible
  • Considering what the person has wanted in the past, their relevant beliefs and values
  • Finding out what their family and close friends say

There is no such list in Northern Ireland, but the same principles will apply.

Restraint and deprivations of liberty

It is lawful to restrain someone lacking capacity in their best interests, provided this is for short periods and not excessive.

However, you cannot take away their freedom of movement altogether without either a court order or – if the person is in a care home or hospital in England or Wales - a 'deprivation of liberty safeguards' (DOLS) authorisation from a local authority, primary care trust or local health board.

Substitute decision-makers

Generally the law allows anyone to make a decision in an incapacitated person’s best interests.

However, certain people are entitled to make ongoing decisions for a person who lacks capacity:

  • An individual who currently has capacity can make a 'lasting power of attorney' that gives someone of their choice the right to make specified decisions on their behalf if they should lose capacity (in England and Wales)
  • A court can make decisions as to someone’s capacity and best interests. In England and Wales these cases usually go to the Court of Protection
  • The court can appoint a substitute decision-maker for someone who clearly lacks capacity, called a 'deputy' (England and Wales)
  • An individual who currently has capacity can stipulate in advance what medical treatment they do NOT want to have if they lose capacity. These 'advance decisions' are legally binding in most circumstances

When a person is unable to manage their welfare benefits, someone else can do it on their behalf in a number of different ways.  Information about these ways, including the role of a deputy and powers of attorney, are explained in our page
"Managing benefits on behalf of somebody else".

First published: Monday 14 May 2012
Updated: Tuesday 31 March 2015