In English law, a unilateral contract involves one party making a promise or offer that becomes binding only when another party completes a specified action or performance.
Unilateral contracts differ from bilateral contracts because acceptance occurs through performance rather than a reciprocal promise. The promisor is bound to fulfil their obligation once the specified action is completed by the promisee.
Carlill v Carbolic Smoke Ball Co (1893): A landmark case establishing enforceability of unilateral contracts when a person acts upon an advertised promise.
Parties offering unilateral contracts must clearly state terms and conditions, as acceptance and contract formation occur immediately upon performance of the specified act.
Understanding unilateral contracts ensures clarity in contractual obligations, particularly for promotional offers, competitions, and reward arrangements.
September 1, 2025
The plaintiff gave information leading to the conviction of murderers after being severely beaten and fearing death. Despite her motive being conscience rather than the advertised £20 reward, the court held she was entitled to recover as she had fulfilled the conditions of the offer. Facts Walter Carwardine was murdered...
September 1, 2025
A father promised to pay £1 weekly for his illegitimate child's maintenance if the mother proved the child would be well looked after and happy. The Court of Appeal held there was sufficient consideration for this promise, even though the mother had a pre-existing legal duty to maintain the child....
August 28, 2025
Dahlia Ltd claimed damages for breach of a unilateral contract, alleging the first defendants promised to exchange written sale contracts for properties if the plaintiffs attended with a banker's draft and signed contract. The Court of Appeal held the unilateral contract fell within Section 40 of the Law of Property...
August 28, 2025
Established principles of unilateral contracts and acceptance by conduct.
August 28, 2025
Carlill v Carbolic Smoke Ball established the legal principle of unilateral contracts, confirming that advertisements may constitute binding offers accepted by performing specific acts.
April 1, 2026
National Case Law Archive
March 31, 2026
National Case Law Archive
March 31, 2026
National Case Law Archive