OT22012 - Interest and Financing: Excluded Loan Relationship debits and credits
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Amounts which are allowable under CTA09\S292 onwards but which are excluded by CTA10\S286 & CTA10\S287 are treated as non-trading debits/credits outside the ring fence (CTA10\S286(5) & CTA10\S287(5)).