"The Tribunal shall decide the appeal on the merits and by reference to the grounds of appeal set out in the notice of appeal."
"(1) Any person with sufficient interest in the outcome may make a request to the Tribunal for permission to intervene in the proceedings."
"(6) If the Tribunal is satisfied, having taken into account the observations of the parties, that the intervening party has a sufficient interest, it may permit the intervention on such terms and conditions as it thinks fit."