SolvedCTM04120 | Corporation tax: trading losses: general: relief for losses carried forward: losses incurred from 1 April 2017: carry-forward against profits of the same trade
From HM Revenue & Customs · Company Taxation Manual
Unrelieved trade losses incurred before 1 April 2017 are carried forward and set against profits of the same trade only (S45).
Unrelieved trade losses incurred after 1 April 2017 will generally be available for set off against total profits under S45A. However, where this is unavailable, relief may be available against profits of the same trade only under S45B.
This will be the case if relief was unavailable under S45A due to
certain conditions of that section,or
restrictions on losses attributable to certain tax reliefs for creative industries (CTA09/S1210 (5), CTA09/S1216DB (5), CTA09/S1217DB (5)).
However, if relief is unavailable under S45A because the trade has ceased, relief will similarly be unavailable under S45B.
If the trade is an oil and gas ring-fence trade, relief for post-1 April 2017 trade losses is only available under S45B to the extent that they are not non-decommissioning losses (CTA10/S303A). Non-decommissioning losses are dealt with in CTA10/S303A to 303D.