(E) THE DEFENDANT MUST HAVE BEEN ENRICHED AT THE CLAIMANT’S EXPENSE
(i) Identifying the Enrichment
Restitution should be awarded by virtue of necessity regardless of the type of enrichment which has been received by the defendant. Even where the alleged enrichment takes the form of goods or services, it will be relatively easy to establish that the defendant has been enriched because necessity will only be established where a reasonable person would have intervened, so it will usually be the case that the defendant will have been incontrovertibly benefited by the intervention, since the defendant will have been saved an inevitable
(ii) Valuing the Enrichment
When assessing the value of an enrichment,  if the enrichment involves a service, a distinction needs to be drawn between three different measures, namely reward, reimbursement, and remuneration. Where the claimant has acted in circumstances ofnecessity it is not appropriate to reward him or her for doing so within the law ofrestitution, simply because a reward does not reverse an unjust enrichment.36 But it will be appropriate to reimburse the claimant’s expenditure incurred in intervening, and it may be appropriate to remunerate the claimant for the provision of his or her services, at least where the claimant is a professional, because these sums will reflect the extent of the defendant’s enrichment.37 So, for example, if the claimant is a vet who saves the life of the defendant’s valuable racehorse in circumstances of necessity after the horse has been injured in an accident, the defendant’s enrichment can legitimately be regarded as including the value of any drugs or materials used by the vet as well as the reasonable value of the vet’s services, since the defendant would have had to pay these sums if the claimant had not intervened. It would not be appropriate, however, to award an additional sum to reward the vet for intervening, at least in a claim grounded on unjust enrichment, since such a sum would not reverse the defendant’s enrichment.
-  37 This was recognized by Ralph Gibson LJ in The Goring  QB 687, 708.