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This case (Dunlop v Selfridge [1945] AC 847) is an important confirmation of the the principle of Privity Of Contract.

Dunlop sold metas to Dew Co., with a term in the agreement that Dew would not sell more cheaply to anyone else, and that Dew would not enter into a contract with anyone else except on the same terms. Dew sold tyres to Selfridge at the stipulated terms, but Selfridge sold them more cheaply. Dunlop brough an action against Selfridge, which failed on the basis that Dunlop had no contract with Selfridge, and was not a party to the contract which had allegedly been breached.

Presumably Dunlop could have taken an action against Dew, who could certainly have taken action against Selfridge.