I've been told there is a legal principle (in UK law, specifically England) that a person cannot be allowed to benefit twice from a court's decision. I've found criminal law which addresses that, and inheritance precedents, but this is a civil case. Specifically an insurance company is trying to avoid paying benefit, relying on an argument that lawful tax avoidance was used to defer tax on certain funds, and so requiring them to pay benefits in relationship to those funds would be the equivalent of allowing the policyholder to benefit twice - first in avoiding tax, and then again by receiving insurance cover for the loss of those funds. I have been told that this inability to benefit twice is a well-established principle of english common law - but I can't find it.
Certainly there's no issue with the insurance company needing to pay the benefit twice, and if they are allowed to benefit by avoiding paying on the policy then they would be benefiting from the policyholder's careful and lawfulapproach to paying only the tax required under the law.
No doubt this is basic law 101, at least I hope so! If anyone could point me to actual law, and also real cases where this might have been applied in any similar way in a civil case, I'd be very grateful.