Also some types of medical treatment do require the patients consent in the form of a signature.

A surprising number, according to my wife (ex-nurse): and often the patient is not in a position to give it, so it is up to their relatives to consent - and there can be considerable pressure brought to bear in this.

A friend's daughter, also a nurse, has spoken about the way in which patients' wishes not to be revived are often flouted.  Because of the targets set by Government, staff do not want the patient's death to be recorded against their ward's figures, so ignore any 'DNR' notes, revive them, and then pass them to another ward.