(1)If part of a trade is to be treated as a separate trade in accordance with section 954(6) or 955(7), just and reasonable apportionments are to be made of receipts, expenses, assets and liabilities.
(2)Subsection (3) applies if—
(a)at the time of an apportionment under subsection (1) it appears that the apportionment is material to the liability to tax (for whatever period) of two or more companies, and
(b)a question arises as to how the apportionment is to be made for the purposes of the liability of those companies.
(3)The question is to be determined in the same way as an appeal, and all the companies concerned are entitled to be a party to the proceedings.