English unjust enrichment law

English unjust enrichment law is a developing area of law in unjust enrichment. Traditionally, work on unjust enrichment has been dealt with under the title of "restitution". Restitution is a gain based remedy, the opposite of compensation, as a loss based remedy. But the event it responds to is the "unjust enrichment" of one person at the expense of another.

A core example (whatever the theoretical analysis) is a mistaken payment. If we have a contract for a book, and the deal is it costs £10, but when you give me the book I mistakenly give you a £20 note, you have been unjustly enriched. If it was the case that you realised I gave you £10 too much, then you have committed the tort of conversion. Unjust enrichment, and the duty to reverse unjust enrichment, operates regardless of awareness. You are strictly liable to reverse it. However, unlike in conversion, there is always a "change of position" defence available. If you (unaware that you now have £10 too much in your wallet) go and consume £10 worth of chocolate, which you would not have done had you not had that extra £10, your position has changed. If I were to demand my £10 back, you could legitimately say, "but then I would be worse off, and that is unfair". This is the change of position defence.

Other than mistakes, a variety of categories of "unjust factors" are said to generate unjust enrichment situations. Undue influence, duress, incapacity and illegality are examples of vitiating factors in contract. Contract law's analysis has been used to explain why courts do not uphold contracts in these situations. These are cases of unjust enrichment.

In the law of trusts, similarly, the ideas of "resulting trusts" and "constructive trusts" conceal unjust enrichment at work. It is a controversial and developing area of English law, and many English lawyers - particularly trust lawyers - deny that unjust enrichment is either useful or necessary.

Unjust enrichment is a developed and coherent field in continental civil law systems. Continental lawyers say someone is unjustly enriched when there is no basis for their possession or title to some right or property. A more correct way of saying it is that someone has been "unjustifiedly enriched". In German, the term is "Ungerechtfertigte Bereicherung" (§812 BGB) and in France the term is "Enrichissement sans cause". English lawyers, however, have been accustomed to identify an "unjust factor". The difference between "unjust factors" and "absence of basis" as a unifying principle has generated a lot of debate, particularly since Peter Birks changed his mind in his second edition of "Unjust Enrichment" (2005) in the Clarendon Law Series, and argued that the continentals had got it right.

The two leading theorists that have revived unjust enrichment were Lord Goff, who produced "Goff and Jones on Restitution" and Professor Peter Birks.

ee also

*"Kelly v. Solari" (1841) 9 M&W 54
*"Dextra Bank & Trust Company Limited v Bank of Jamaica"
*Peter Birks