Unjust Enrichment in UK Law

My Lords, there is no general doctrine of unjust enrichment recognised in English law. It is a convenient way of describing a transfer of rights from one person to another, without assignment or assent of the person from whom the rights are transferred and which takes place by operation of law in a whole variety of widely different circumstances.

But I think it should be recognised that one is here concerned with a restitutionary remedy and that the appropriate questions are therefore, first, whether the defendant would be enriched at the plaintiff's expense; secondly, whether such enrichment would be unjust and thirdly, whether there are nevertheless reasons of policy for denying a remedy. But I think it should be recognised that one is here concerned with a restitutionary remedy and that the appropriate questions are therefore, first, whether the defendant would be enriched at the plaintiff's expense; secondly, whether such enrichment would be unjust and thirdly, whether there are nevertheless reasons of policy for denying a remedy.

It is clear that any civilised system of law is bound to provide remedies for cases of what has been called unjust enrichment or unjust benefit, that is to prevent a man from retaining the money of or some benefit derived from another which it is against conscience that he should keep.

The enrichment will be at the expense of the claimant if in reality it was the claimant's money which effected the improvement. The remedy is flexible and adaptable to produce a just result. Within this framework, the remedy is discretionary in the sense that at each stage it is a matter of judgment whether on the facts the necessary elements are fulfilled.

As Professor Birks pointed out, the availability of money to use is not unequivocally enriching in the same degree as the receipt of money: Unjust Enrichment, 2nd ed, p 53. It is an imperfect way of measuring the time value of what was received prematurely. Restitution requires that the entirety of the time value of the money that was paid prematurely be transferred back to Sempra by the Revenue.

At present I do not wish to state the principle any less broadly than this: that the defence is available to a person whose position has so changed that it would be inequitable in all the circumstances to require him to make restitution, or alternatively to make restitution in full.

Having considered the wide ranging material put to me by Mr Matthias (wide ranging despite the relatively short period of time that this case took—argument on all issues took less than a day), it seems to me that it has not been established that the authorities have yet moved to a position in which it can be said that there is a freestanding claim of unjust enrichment in the sense that a claimant can get away with pleading facts which he says leads to an enrichment which he says is unjust.