"It is the responsibility of an Adjudicator or Special Adjudicator to control the proceedings before him or her and to ensure that both parties to an appeal are given a fair and proper opportunity to present their cases. It is also the responsibility of the Adjudicator to ensure that the proceedings are conducted with due regard to the rules of natural justice. There is no rule of law or evidence which restricts a Presenting Officer from asking questions in cross-examination which are not specifically raised by the refusal letter, nor is there any obligation upon an Adjudicator to impose such a restriction."