There is an Act called the Mental Capacity Act (2005) which confirms in legislation that it should be assumed that an adult (aged 16 or over) has full legal capacity to make decisions for themselves (the right to autonomy) unless it can be shown that they lack capacity to make a decision for themselves at the time the decision needs to be made. This is known as the presumption of capacity. The Act also states that people must be given all appropriate help and support to enable them to make their own decisions or to maximise their participation in any decision-making process
The underlying philosophy of the Mental Capacity Act (2005) is to ensure that any decision made, or action taken, on behalf of someone who lacks the capacity to make the decision or act for themselves is made in their best interests
If someone doesn’t have the mental capacity to carry out advance care planning then discussion with your family, GP, nurse or social worker can help determine what would be in your ‘Best Interests’.
However, previous advance care planning activity such as Advance Statements, and Lasting Power of Attorney can help guide decisions.
For more information, look at this website