(1) Subject to this section, group relief shall be given only if the surrendering company and the claimant company are members of the same group, or fulfil the conditions for relief for a consortium, throughout the whole of the surrendering company's accounting period to which the claim relates and throughout the whole of the corresponding accounting period of the claimant company.
(2) Where on any occasion 2 companies become or cease to be members of the same group, then, for the purposes specified in subsection (3), it shall be assumed as respects each company that on that occasion (unless a true accounting period of the company begins or ends then) an accounting period of the company ends and a new one begins, the new accounting period to end with the end of the true accounting period (unless before then there is a further break under this subsection) and -
(a) that the losses or other amounts of the true accounting period are apportioned to the component accounting periods on a tim
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