Decision making for setting new policies is a challenging process as the current policy making system is utterly flawed. A policy is introduced by the decision maker when the problem domain was fully consulted by experts in the field. Not always all the consultants and advisers agree on details or even basics of such a course of action. The need for an intelligent predictive system is emerging. Policy making on environmental issues are even shoddier as the environmental systems are habitually complex, and adaptive; and introduction of new technologies can easily affect the guiding strategies already taken. This paper outlines the principles of Knowledge Management Systems. It then reflects on Influence Diagrams’ suitability for construction of such an information system through the use of the London Plan case study. An application of such a system is outlined by means of a probabilistic knowledge based IS which is developed by Influence Diagrams and can be utilized as an Environmental policy modeler and/or DSS.