CG65958 | Losses: loans to traders: irrecoverability: terms of loan/acts of lender
From HM Revenue & Customs · Capital Gains Manual
In accordance with TCGA92/S253 (12), you should not regard any amount as having become irrecoverable where it has so become in consequence of
the terms of the loan itself,
or
arrangements of which the loan forms part,
or
any act or omission by the lender.
These conditions are intended as anti-avoidance protection, to exclude from the relief a variety of devices ranging from the simple gift dressed up as a loan to more sophisticated schemes such as the siphoning of resources out of a company which then becomes unable to repay its loan.