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.

When judges say that the charge is "kept alive" for the benefit of the plaintiff, what they mean is that his legal relations with a defendant who would otherwise be unjustly enriched are regulated as if the benefit of the charge had been assigned to him. When judges say that the charge is "kept alive" for the benefit of the plaintiff, what they mean is that his legal relations with a defendant who would otherwise be unjustly enriched are regulated as if the benefit of the charge had been assigned to him.

The recovery of money in restitution is not, as a general rule, a matter of discretion for the court. A claim to recover money at common law is made as a matter of right; and even though the underlying principle of recovery is the principle of unjust enrichment, nevertheless, where recovery is denied, it is denied on the basis of legal principle.

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.

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. I do not think that such an award would be consistent with principle. Simple interest is an artificial construct which has no relation to the way money is obtained or turned to account in the real world. It is an imperfect way of measuring the time value of what was received prematurely.

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.