This section applies where X is greater than Y in the case of an accounting period of a company and a site, where—

• X is the closing balance of unactivated allowance for the accounting period and the site;

• Y is the company's relevant income for the accounting period from that site.

An amount equal to the difference between X and Y is treated as onshore allowance held by the company for that site for the next accounting period (and is treated as held with effect from the beginning of that period).