3. Existing duties and consideration (Public/Legal/Contractual duties)
Basic rule: If a party just performs only their public, legal or contractual duty then a later promise to pay for that is unenforceable due to the lack of consideration.
Case (Pub/Legal): "Collins v Godefroy". In this case claimant had been summoned to court and was promised to be paid by the defendant. However defendant refused to pay when he turned up ... unenforceable. Case (Contractual): "Stilck v Myrick". A ship sailed to the Baltic, but 2 members absconded ... the promise to share the wages was unenforceable and the crew members action failed. AO2: This seems logical but it allows people to break their promises.
Exception: If a party performs above and beyond their public/legal/contractual duty then a later promise to pay that is enforceable due to good consideration. Case (Pub/Legal): "Glassbrook v Glamorgan". In this case Glassbrook asked the police to provide static police presence around the mine. However, the police said mobile patrol would be enough ... Glassbroook refused to pay. Held: Police went above and beyond and ... had to pay = enforceable. Case (Contractual): "Hartley v Ponsonby". Facts very similar to "Stilck v Myrick" but 17 members absconded of a crew of 35 ... captain had to share the wages = enforceable.