Where the promise is doing something which is a duty imposed by some public obligation, there is a reluctance to allow this to be used as the basis of a contract...The difficulty is in discerning whether the refusal to enforce such a contract is on the basis that it is vitiated as being contrary to public policy, or because the consideration which has been provided is invalid.' - Richard Stone 'The Modern Law of Contract' p98 Per Denning LJ in Williams v Williams: "...a promise to perform an existing duty is, I think, sufficient consideration to support a promise, so long as there is nothing in the transaction which is contrary to public policy." The quotes above from Richard Stone and Denning LJ both refer to public policy. Do you think the reasoning behind the decisions was ultimately based on public policy? Give reasons for your conclusion