# Unjust enrichment overview

> **Key takeaway:** Enrichment + at C's expense + unjust factor + defences (Banque Financière structure). Mistake/failure of basis common. Change of position (Lipkin Gorman). Distinct from contract/tort. ITC on multi-party 'expense'.

- **Jurisdiction:** England & Wales
- **Practice area:** Commercial
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/Commercial/unjust-enrichment-overview
- **Keywords:** unjust enrichment, restitution, mistake, change of position, Lipkin Gorman, failure of basis, quantum meruit, Banque Financière

## What is this about?

Unjust enrichment is a common-law category of claim requiring enrichment of the defendant at the claimant's expense, in circumstances that are unjust, subject to defences. It underpins restitution of mistaken payments and many failed-contract recoveries, distinct from contract and tort.

## What is the core rule?

A claim in unjust enrichment generally requires: (1) enrichment; (2) at the claimant's expense; (3) an unjust factor (e.g. mistake, failure of basis, duress, undue influence, ultra vires demand); and (4) no available defence (change of position, estoppel, ministerial receipt, limitation). Leading modern framework cases emphasise structured analysis (Banque Financière; Investment Trust Companies; Swynson themes). Quantum meruit/quantum valebat often operate as enrichment measures for services/goods.

## What are the elements or test?

1. Identify enrichment (money, services, discharge of debt)?
2. At claimant's expense — corresponding loss/transfer link?
3. Which unjust factor?
4. Defences: change of position (good faith expenditure)?
5. Is a better contractual or proprietary analysis available?

## Which authorities matter?

- **Banque Financière de la Cité v Parc (Battersea) Ltd [1999] 1 AC 221** — House of Lords four-question approach often used as a starting template.
- **Lipkin Gorman v Karpnale Ltd [1991] 2 AC 548** — Restitution against innocent recipient; change of position defence recognised.
- **Investment Trust Companies v HMRC [2017] UKSC 29, [2018] AC 275** — Supreme Court on 'at the expense of' in multi-party tax enrichment chains.
- **Kleinwort Benson Ltd v Lincoln CC [1999] 2 AC 349** — Mistake of law can ground restitution (subject to defences and later statutory contexts).

## How does this apply in practice?

Do not plead unjust enrichment to rewrite a bad bargain where a valid contract allocates risk. Public authority ultra vires payments have specialised Woolwich routes. Pair with tracing notes for proprietary follow-on.

## What are common pitfalls?

- Skipping the unjust factor and arguing free-floating 'unfairness'
- Ignoring change of position
- Double recovery with contractual damages
- Mispleading enrichment in pure services cases without evidencing value

## When would a practitioner use this?

Mistaken payments, failed joint ventures, and restitution after void contracts.

## Quick reference

Enrichment + at C's expense + unjust factor + defences (Banque Financière structure). Mistake/failure of basis common. Change of position (Lipkin Gorman). Distinct from contract/tort. ITC on multi-party 'expense'.

---

*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*