The MCA has five guiding principles, which are:

1. A person must be assumed to have capacity unless it is established that he lacks capacity.
2. 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.
3. A person is not to be treated as unable to make a decision merely because he makes an unwise decision.
4. 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.
5. 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.

A person is said to lack ‘mental capacity’ if s/he is unable to make a decision in relation to a particular matter ‘because of an impairment of, or a disturbance in the functioning of, the mind or brain’ (s2 MCA).  The abilities required  to make a particular decision are as  follows:

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). (s3 MCA)

If a person ‘lacks capacity’ in relation to a matter then other people can make decisions about that matter for them in their ‘best interests’.  Section 4 of the MCA sets out the ‘best interests checklist’, which tells decision makers what they have to think about when making best interests decisions.  They must consider the person’s past and present wishes and feelings, values and beliefs.  They must – so far as practicable and appropriate – consult with others engaged in caring for that person or interested in their welfare . Having followed these steps and taken these matters into account, the person making the decision about best interests must employ what the Court has described as a ‘balance sheet’ approach, which means weighing the likely advantages for the person against the likely disadvantages. Only if the ‘account’ is ‘relatively significantly in credit’, will the intervention be in the person’s best interests.  The ‘balance sheet was developed in a case called Re A (Medical Treatment: Male Sterilisation) (2000); a more recent example can be seen in NHS Trust v K & Ors (2012).  The MCA’s ‘best interests’ approach is not the same as ‘substituted judgment’ which is used in some other jurisdictions because, although it tries to look at things from the person’s point of view, their past or present wishes can be outweighed by other factors (Aintree University Hospitals NHS Foundation Trust v James, 2013).

The MCA also allows for restraint to prevent harm to a person who lacks capacity, provided  that the act is a proportionate response to the likelihood of them suffering harm and the severity of that harm.  Restraint is defined as the use of force, or threat of use of force, to secure the doing of something which the relevant person resists, or if it involves restricting a person’s liberty whether or not they resist (s6 MCA).  If it involves depriving them of their liberty, then deprivation of liberty procedures  will need to be used.If there is a serious dispute or it falls into a small category of ‘special cases’ then an application to the Court of Protection should be made.