Money had and Received in UK Law

20,000 in a trip round the world, which he would not have undertaken without the gift, it seems to me that the donee has altered his position on the faith of the gift and that he is not unjustly enriched when the victim of the theft seeks restitution.

Furthermore, it appears that in these cases the action for money had and received is not usually founded upon any wrong by the third party, such as conversion; nor is it said to be a case of waiver of tort. It is founded simply on the fact that, as Lord Mansfield said, the third party cannot in conscience retain the money — or, as we say nowadays, for the third party to retain the money would result in his unjust enrichment at the expense of the owner of the money.

The answer must be that, where an innocent defendant's position is so changed that he will suffer an injustice if called upon to repay or to repay in full, the injustice of requiring him so to repay outweighs the injustice of denying the plaintiff restitution.

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.

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.

In one word, the gist of this kind of action is that the Defendant upon the circumstances of the case is obliged by the ties of natural justice and equity to refund the money." Lord Mansfield does not say that the law implies a promise; the law implies a debt or obligation which is a different thing. In fact he denies that there is a contract; the obligation is as efficacious as if it were upon a contract.

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.