A collateral contract is a contract that is entered into for the purpose of inducing the parties to enter into another separate contract. For instance, where Party A purchases goods from Party B and A uses the Point of Sale (POS) machine as provided by B to pay for the purchase, the contract of purchase of goods between A and B, is different from the contract between the POS company and party B. Where there is a breach emanating from the POS company in paying B, if A was in good financial standing and he actually paid the POS company, A can sue the POS company in order to show his credit worthiness. SHANKLIN PIER LTD v. DETEL PRODUCTS LTD. (1951) 2 All ER 471.
Where there is a breach of contract in the second ambit of the contract as constituting a collateral contract, a party that was privy in the first contract and not a privy in the second contract, can sue for the breach in the second contract.