# Mistake in contract: common, mutual, and unilateral

> **Key takeaway:** Common mistake: strict, fundamental, no risk allocation (Bell; Great Peace). Mutual: no matching agreement. Unilateral as to terms: need other party's knowledge (Smith v Hughes). Identity: written named party vs face-to-face (Shogun). Mistake ≠ misrepresentation ≠ frustration.

- **Jurisdiction:** England & Wales
- **Practice area:** Commercial
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/Commercial/mistake-in-contract
- **Keywords:** mistake, common mistake, unilateral mistake, Great Peace, Bell v Lever Brothers, Shogun Finance, identity, void contract

## What is this about?

Mistake can prevent a contract from forming or render it void (or, more rarely, voidable in equity). English law is cautious: bad bargains are not undone merely because a party was mistaken about value. The important categories are common mistake as to a shared assumption, mutual misunderstanding of terms, and unilateral mistake known to the other party (including identity mistakes).

## What is the core rule?

A contract may be void for common mistake where, unknown to both parties, a shared fundamental assumption is false and the contract allocates neither risk nor solution — the modern common-law test is strict (Bell v Lever Bros; Great Peace Shipping). Mutual mistake as to terms may mean no correspondence of offer and acceptance. Unilateral mistake as to terms generally does not avoid the contract unless the non-mistaken party knew of the mistake (or, in limited identity cases, the contract is void or voidable depending on whether it was face-to-face or written with a rogue — Shogun Finance; Lewis v Averay line).

## What are the elements or test?

1. Classify the mistake: common (same shared error), mutual (cross-purposes), or unilateral
2. Common mistake: is the assumption fundamental; does the contract allocate the risk; is performance essentially different (Great Peace)?
3. Mutual mistake: was there a genuine offer and acceptance on the same terms?
4. Unilateral mistake as to terms: did the other party know of the mistake?
5. Identity mistake: written contract with identified rogue vs face-to-face dealing — different outcomes for void/voidable and third-party title

## Which authorities matter?

- **Bell v Lever Brothers Ltd [1932] AC 161** — House of Lords foundation for common mistake; the mistake must be fundamental to the identity of the contract subject-matter, not merely a bad bargain.
- **Great Peace Shipping Ltd v Tsavliris Salvage (International) Ltd [2002] EWCA Civ 1407, [2003] QB 679** — Court of Appeal rejects a broad equitable jurisdiction to rescind for common mistake separate from the strict common-law test; performance must be essentially different.
- **Smith v Hughes (1871) LR 6 QB 597** — Classic objective approach to terms and unilateral mistake: the contract is judged by outward appearance, subject to knowledge of the other's mistake as to terms.
- **Shogun Finance Ltd v Hudson [2003] UKHL 62, [2004] 1 AC 919** — Written hire-purchase with a named hirer: identity of the named party is fundamental; face-to-face cases remain more fact-sensitive for voidable title analysis.

## How does this apply in practice?

Do not confuse contractual mistake with misrepresentation (a false statement inducing the contract) or with frustration (supervening events after formation). Non est factum is a narrow, separate doctrine. Rectification is an equitable remedy for recording error, not a general escape from a bad deal.

## What are common pitfalls?

- Treating a mistake as to quality or value as automatically fundamental
- Relying on pre-Great Peace equitable common-mistake rescission as if it were free-standing and broad
- Mixing face-to-face and written-identity authorities without reading Shogun carefully
- Pleading mistake where the real complaint is misrepresentation or non-disclosure

## When would a practitioner use this?

Relevant in asset sales where the subject no longer exists, crossed negotiations on terms, and fraud/identity theft supply chains affecting title.

## Quick reference

Common mistake: strict, fundamental, no risk allocation (Bell; Great Peace). Mutual: no matching agreement. Unilateral as to terms: need other party's knowledge (Smith v Hughes). Identity: written named party vs face-to-face (Shogun). Mistake ≠ misrepresentation ≠ frustration.

---

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