Privity - only those who are a party to the contract and are bound by it can sue under it (Dunlop v Selfridge)
Courts will allow exceptions to this rule e.g. Agency (Jackson).
Exclusion clauses only protect parties to the contract, not subcontractors (Scruttons)
The courts may find a second contract alongside the main one - Collateral contracts (Shanklin pier).
Restrictive convenants remain with the land to which they refer (Tulk).
The Contracts (Right of Third Parties) Act 1999 gives those who benefit from a contract but are not a party to it the right to sue under that contract.
This is provided
the third party is expressly named or fits a description
the contract provided for a third party to enforce it
the contract is an attempt to benefit the third party