What is the effect of a person not being aware of the facts of a criminal case?

In SSHD v. M.B., above, at paragraph 35, Lord Bingham commented on the "grave disadvantages" of the person affected not been aware of the case against him. He noted that the reason is obvious: In any ordinary case, the client instructs his advocate what his defence is to the charges made against him, briefs the advocate on the weaknesses and vulnerability of the adverse witnesses, and indicates what evidence is available by way of rebuttal. This is a process which may be impossible to adopt if the control person does not know the allegations made against him and cannot therefore give meaningful instructions, and the special advocate, once he knows what the allegations are, cannot tell the controlled person or seek instructions without permission, which in practice (as I understand) is not given.