Share Loss Relief: background: allowing relief
For individuals, amounts which qualify for Share Loss Relief are deducted from net income either for the year of the loss or the previous tax year, or both years. The claim must specify in which year or years relief is claimed. There is more detailed guidance at VCM74030.
For companies, amounts which qualify for Share Loss Relief are deducted firstly in computing income chargeable to corporation tax in the accounting period in which the loss arose. If there is unused relief, the claim may require it to be deducted from income in an accounting period falling wholly or partly within the twelve months immediately preceding the accounting period in which the loss accrued. Where relief is claimed in an earlier period, the amount of relief is limited to the profits of that earlier period which are attributable to the preceding twelve month period using time-apportionment (CTA10/S72).
Note that relief must be allowed to a company in the period of loss before any relief may be given in an earlier period and contrast this with the case for an individual, when relief may be claimed wholly in an earlier year to the exclusion of the year of loss.
There is more detailed guidance at VCM77040.