Written contracts should usually set out what each party has promised to do for the other but there may, of course, also be unwritten, implied, terms to be discovered by a legal tribunal. There might even be other associated unwritten obligations in tort, owed to third parties, perhaps the tricky topic of a duty (or not) to warn.

In Cleightonhills v Bembridge Marine Ltd, a personal injuries claim involving an inadequately designed gantry platform, Mr Justice Akenhead had to consider when a duty of care to warn might arise in tort. There can be little doubt, he said, that, subject to the circumstances, a failure to warn of potential danger to human beings might give rise to a breach of any duty of care owed to a third party by a party who knows of the danger. Where the parties are in contract, the duty to warn may extend to dangers of which the party in question should have been aware by reason of its involvement as, for instance, a contractually appointed surveyor. In tort alone, however, any duty to warn may not in fact extend to warning the class of people who might be affected by the danger; it may be limited to warning the other party to the contract or the local authority.

Cleightonhills v Bembridge Marine Ltd & Ors [2012] EWHC 3449