This is a specific instruction that you give when you still have mental and physical capacity about any treatment you want to refuse in the future.
If this is done correctly in accordance with the Mental Capacity Act 2005 medical professionals must follow your wishes even if they consider it is not in your best interests. This does not need to be in writing unless you are wanting to refuse lifesaving treatment in which case it is signed and witnessed as if it were a Will and it must clearly state you wish to refuse treatment even if your life is at risk.
The directive will only take effect at a time when you do not have the mental capacity any more to make these decisions yourself. It cannot be used however to request treatment nor to refuse basic care. At Hindle Campbell Law we are very happy to talk you through your options should this be a concern for you and explain the processes involved.