1(1)In relation to any oil field—
(a)the first claim period is whichever of the following periods the responsible person elects, namely the period ending at the end of June following the determination of the field or the period ending at the end of December following that determination (including, in either case, an unlimited time prior to that determination);
(b)each subsequent claim period is whichever of the following periods the responsible person elects, namely the period of six months or the period of twelve months from the end of the preceding claim period:
Provided that unless and until the responsible person elects the period of six months from the end of any particular claim period, the claim period next after that claim period shall be taken to be the period of twelve months from the end of it.
(2)An election under this paragraph must be made by notice in writing to the Board.