"It is axiomatic that justice must not only be done, but be seen to be done. There may be rare circumstances in which it is appropriate for an Industrial Tribunal to wish to see the parties' representatives in the absence of the parties themselves. But it seems to us that this was not an occasion for taking that step. If the tribunal had anything to say at that stage of the proceedings about their state of mind in relation to the prospects of success, then it was their duty, in our view, to do it to the parties themselves in the presence of their representatives."