Answer
A deputy is a person that the Court of Protection appoints to make decisions for someone who does not have the mental capacity to make decisions for themselves regarding their personal welfare, property and other affairs. The Court of Protection will outline exactly what responsibilities a deputy has which is decided on a case-by-case basis.
There are, however, several things that a deputy is not allowed to do. These include: refusing any treatment that would help you stay alive should you develop a life–threatening condition, or using force to stop you from doing something or going somewhere. A deputy also cannot object to a decision made by a solicitor acting under a Lasting Power of Attorney.
If a deputy does not act in your best interests, goes beyond their powers or becomes incapable of acting as your deputy, the Court of Protection can remove them or change the type of decisions that they can make on your behalf.