"The Tribunal, after taking into account the observations of the parties, may at any time determine whether its proceedings are to be treated, for purposes connected with ..." – I paraphrase here – any matter connected with those proceedings: "... as proceedings in England and Wales, in Scotland or in Northern Ireland and shall instruct the Registrar to notify the parties of its determination."
"In making a determination under sub-rule (1) the Tribunal may have regard to all matters which appear to it to be relevant and in particular the part of the United Kingdom where – (a) any individual party to the proceedings is habitually resident or has his head office or principal place of business; (b) the majority of the parties are habitually resident or have their head offices or principal places of business; (c) any agreement, decision or concerted practice to which the proceedings relate was made or implemented or intended to be implemented; (d) any conduct to which the proceedings relate took place."