(1) An allowance or charge under this Chapter shall be made to or on a company in taxing the company's trade if -
(a) the company is carrying on a trade the profits or gains of which are or, if there were any, would be, chargeable to corporation tax for the chargeable period for which the allowance or charge is made, and
(b) at any time in the chargeable period or its basis period the capacity rights in question, or other rights out of which they were granted, were used for the purposes of that trade.
(2) Except where provided for in subsection (1), an allowance under this Chapter shall be made by means of discharge or repayment of tax and shall be available against income from capacity rights, and a charge under this Chapter shall be made under Case IV of Schedule D.