Cheshire and Pifoot in their book on "Law of Contract" 3rd Edn., observe at page 280 thus : "The public interests which it is designed to protect are so comprehensive and haterogeneous, and opinions as to what is injurious must of necessity vary so greatly with the social and moral convictions, and at times even with the political views, of different judges, that it forms a treacherous and unstable ground for legal decision. These questions have agitated the Courts in the past, but the present state of the law would appear to be reasonably clear. Two observations may be made with some degree of assurance. First, although the rules already established by precedent must be moulded to fit the new conditions of a changing world, it is no longer legitimate for the Courts to invent a new head of public policy. A judge is not free to speculate upon what, in his opinion, is for the good of the community. He must be content to apply, either directly or by way of analogy, the principles laid down in previous decisions. He must expound, not expand, this particular branch of the law. Secondly, even though the contract it one which prima facie falls under one of the recognized heads of public policy, it will not be held illegal unless its harmful qualities are indisputable. The doctrine, as Lord Atkin remarked in a leading case, "should only be invoked in clear cases in which the harm to the public is substantially incontestable, and does not depend upon the idiosyncratic inferences of a few judicial minds. In popular language the contract should be given the benefit of the doubt."