Carlill v Carbolic Smoke Ball Co [1893] 1 QB 256
This decision remains the foundational authority on unilateral offers and acceptance by conduct. The defendants advertised that they would pay £100 to anyone who contracted influenza after using their smoke ball as directed, and deposited £1,000 as evidence of sincerity. Mrs Carlill used the product, contracted influenza, and claimed the reward. The Court of Appeal held that the advertisement constituted an offer (not a mere puff) capable of acceptance by anyone who performed the specified act. Acceptance did not require communication of intent to accept; performance of the conditions was sufficient. Bowen LJ's judgment clarified that offers may be made to the world at large and that the deposit of money negatived any suggestion of mere puffery. The case illustrates how the objective test accommodates unilateral contracts and remains vital for understanding reward cases, promotional schemes, and acceptance by conduct.
Adams v Lindsell (1818) 1 B & Ald 681
This early decision established the postal rule. The defendants wrote to the claimants offering to sell wool, requesting a reply 'in course of post'. The letter was misdirected, delaying its arrival. The claimants posted acceptance immediately upon receipt, but before this acceptance arrived, the defendants, hearing nothing, sold the wool elsewhere. The court held that the contract was concluded when the claimants posted acceptance. The rule allocates the risk of postal delay to the offeror and privileges the offeree's reliance interest. Though controversial and increasingly confined, Adams v Lindsell remains good law for non-instantaneous acceptances.
Entores Ltd v Miles Far East Corporation [1955] 2 QB 327
Denning LJ's judgment established that instantaneous communications (here, telex) are governed by the receipt rule, not the postal rule. Acceptance is effective when and where it is received by the offeror. The decision reflects commercial sense: where communication is immediate, there is no justification for the postal rule's allocation of risk. Denning LJ acknowledged qualifications where the offeree reasonably believes acceptance has been received but it has not (e.g., due to offeror's faulty equipment), though such cases are rare. The principle applies to telephone, fax, email, and instant messaging. The case was approved and refined in Brinkibon Ltd v Stahag Stahl [1983] 2 AC 34, which emphasised that the precise moment and place of receipt may depend on business practice and reasonable contemplation.
Butler Machine Tool Co Ltd v Ex-Cell-O Corporation (England) Ltd [1979] 1 WLR 401
The 'battle of the forms' arises where each party seeks to contract on its own standard terms. Butler offered to sell a machine tool on its standard terms, which included a price variation clause. Ex-Cell-O replied with an order on its own terms, which excluded price variation, and included a tear-off acknowledgment slip. Butler returned the slip and delivered the machine. When Butler sought to invoke the price variation clause, the Court of Appeal held that Ex-Cell-O's order was a counter-offer that Butler had accepted by returning the slip and performing. Lord Denning MR suggested courts should consider the documents as a whole and imply terms to fill gaps, but the majority (Lawton and Bridge LJJ) applied traditional offer–counter-offer analysis. The last shot rule—the last set of terms before performance governs—prevailed, though its mechanical application is increasingly criticised and courts now show greater willingness to identify core agreed terms.
Hyde v Wrench (1840) 3 Beav 334
Wrench offered to sell a farm for £1,000. Hyde responded offering £950, which Wrench rejected. Hyde then purported to accept the original offer of £1,000. The court held that Hyde's £950 offer was a counter-offer that destroyed the original offer, so no contract arose. The rule requires acceptance to be a 'mirror image' of the offer. The case establishes the destructive effect of counter-offers and remains central to formation analysis, though it is qualified by Stevenson, Jacques & Co v McLean, which distinguishes a mere inquiry from a counter-offer.
Pharmaceutical Society of Great Britain v Boots Cash Chemists (Southern) Ltd [1953] 1 QB 401
Boots operated a self-service pharmacy. The Pharmaceutical Society alleged that this violated the Pharmacy and Poisons Act 1933, which required sales of certain drugs to occur under a pharmacist's supervision. The Court of Appeal held that the display of goods on shelves was an invitation to treat, not an offer, and the customer made an offer by presenting goods at the till, which the pharmacist (present at the till) could accept or reject. This preserved the retailer's freedom to decline sales and ensured compliance with the statute. The principle applies broadly to retail displays, vending machines (by analogy), and online shopping baskets (before checkout).
RTS Flexible Systems Ltd v Molkerei Alois Müller GmbH & Co KG (UK Production) [2010] UKSC 14
RTS contracted to automate Müller's factory. The parties exchanged draft terms but never executed a formal written contract, though RTS commenced and largely completed performance. Müller argued that the lack of signed agreement meant no contract existed. The Supreme Court held that a binding contract could be found from the parties' conduct, correspondence, and the commercial context. Lord Clarke emphasised that the court must apply an objective test to all the circumstances, asking whether the parties intended to be bound even in the absence of a signed document. The decision illustrates judicial pragmatism: rigid insistence on offer–acceptance formalities may frustrate commercial expectations. It reaffirms that courts will give effect to objectively manifested agreement, drawing on implied terms and conduct where necessary.