(1) Where a person incurs qualifying expenditure on the purchase of a qualifying quota and, before the end of the writing-down period, any of the following events occurs -
(a) the person sells the qualifying quota or so much of the quota as the person still owns;
(b) the qualifying quota comes to an end or ceases altogether to be used;
(c) the person sells part of the qualifying quota and the net proceeds of the sale (in so far as they consist of capital sums) are not less than the amount of the qualifying expenditure remaining unallowed;
no writing-down allowance shall be made to that person for the chargeable period related to the event or any subsequent chargeable period.
(2) Where a person incurs qualifying expenditure on the purchase of a qualifying quota and, before the end of the writing-down period, either of the following events occurs -
(a) the qualifying quota comes to an end or ceases altogether to be used;
(b) the person sells all of the qualifying quota or so much of that
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