BIM40085 | Receipts: general: possible future repayment
From HM Revenue & Customs · Business Income Manual
It should be noted that the mere fact that income may, in certain later circumstances, have to be repaid, does not preclude its treatment as a trade receipt (Smart v Lincolnshire Sugar Co Ltd [1937] 20 TC 643).
Guidance specific to the treatment of commissions received by insurance brokers on ’indemnity terms' is given at BIM40680.