CH146280 | Interest: Repayment interest: Special provisions for start dates: Relief for losses and averaging

From HM Revenue & Customs · Compliance Handbook

You must check whether, and from which date, the FA 2009 interest rules apply to the tax or duty you are dealing with. See CH140160 for full details.

A special provision changes the repayment interest start date from the general rule, see CH146040, where a person makes a claim to

calculate loss relief as though it was given in an earlier year, see SACM11005 (TMA70/SCH1B/PARA2), or
average the profits of farmers etc over two consecutive years, see BIM84000 (ITTOIA05/PART2/CHAPTER16).

The repayment interest start date is 31 January following the year that is the later year in relation to the claim.

See CH146300 for examples.