Williams v Roffey Bros [1991] 1 Q.B. 1 1. : All three judges (Glidewell LJ, Russel LJ, Purchas LJ) rely on the idea that the defendants obtained a 'practical benefit' as a result of the plaintiff's promise to perform his existing contractual duty. What is this practical benefit? Check back through the judgments and try to identify the various explanations offered by the judges.