“(a) to direct that the decision, so far as it remains in force, is to cease to have effect from such time as the tribunal may direct; (b) to require the Commissioners to conduct, in accordance with the directions of the tribunal, a review or further review as appropriate of the original decision; and (c) in the case of a decision which has already been acted on or taken effect and cannot be remedied by a review or further review as appropriate, to declare the decision to have been unreasonable and to give directions to the Commissioners as to the steps to be taken for securing that repetitions of the unreasonableness do not occur when comparable circumstances arise in future”