At the heart of the Mental Capacity Act 2005 (MCA) lies ‘best interests’. As we have seen, one of the key principles of the Act is that, if someone lacks capacity, any decision made on their behalf must be in their best interests:

Section 4 of the MCA concerns best interests and sets out certain steps that must be followed in order to determine a person's best interests. Before considering these steps, however, it is worth pausing to reflect on just what the notion of ‘best interests’ might mean. This should help us to understand the approach taken in the Act.

What are ‘best interests’?

Whereas the MCA defines what it means by a ‘lack of capacity’, it does not define ‘best interests’. The Code of Practice (Department for Constitutional Affairs, 2007) gives some reasons why this is so. ‘Best interests’ is not defined in the Act:

The implication is that trying to define ‘best interests’ would be a hopeless task. Clearly, the notion implies whatever is best for the person. But it is not immediately apparent how this should be determined. For one thing, it might depend on the perspective from which ‘what is best’ is judged. We can easily imagine a scenario in which what the person thinks is best might differ from what the person's family thinks is best (say, for instance, the person has cancer and has been offered chemotherapy that will not cure the disease but will prolong life by a matter of a few months). We can also imagine a patient and a doctor having different views about what might be best (perhaps, in some other form of cancer, there are good grounds for thinking that radical surgery would be curative, so the doctors are encouraging it).