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This case (Harbutt's Plasiticine v Wayne Tank [1970] 1 QB 447) founded the principle (now not widely used) that an Exclusion clause was invalidated by a significant breach of contract. Harbutt's contracted Wayne Tank to build a storage facility for hot liquids; the pipework was constructed of inappropriate material which melted on the first use, set fire to the plant, and burned it to the ground. Wayne Tank tried to rely on a clause limiting its liability, and which the plaintiffs had acknowledged on signing the contract. Denning LJ ruled that the defendants had breach the contract so significantly that it was effectively void; therefore the exclusion clause -- like the rest of the contract -- did not exist. Therefore the defendents owed the usual common law duty of care to the defendents, which they negligently discharged.

Denning's opposition to exclusion clauses was well-known, and this case was widely cited in support of unfair exclusions. However, it was overruled by the House of lords in , and the law remains that if two organizations of equal bargainging power enter into a contract, they must remain bound by its terms even if one of them breaches the contract (see: Photo productions v securicor ltd (1980)).