An Advance Directive (also known as a Living Will or Advance Decision) is a legal document that can help you to ensure your ongoing well-being is taken care of when you cannot do so yourself.
This is because Advance Directives allow a person to specify what actions may be taken regarding their health if you are unable to make decisions in this area for yourself due to your illness or other health-related incapacity.
The Mental Capacity Act 2005 provides that an Advance Directive may be made so decisions may be made for you regarding your health-related issues that may arise in the future. Principally, any Advance Directives that are put into place mean that you can refuse particular medical treatment when you lack mental capacity to do so yourself.
To be legally binding upon those that would provide you with medical treatment then your Advance Directives need to be specific about the treatment to be refused and when that refusal is to apply. Moreover, for an Advance Directive to be valid, it is necessary for you to be mentally competent under the Mental Capacity Act 2005, to have been an adult and understood the decision when you signed it.
The need to seek professional advice to produce Advance Directives is then only further emphasised where you want to refuse life-prolonging treatment. This is because this kind of decision needs to be recorded both in writing and witnessed by an independent third party.
Then, as has already been stated, any Advance Directives regarding the refusal of life-prolonging treatment is legally binding so long as you are an adult and were both properly competent and informed when coming to your decision.