Power is the ability to get things done by others. The principle of power is to punish and reward. Power can exist with or without authority. For instance an armed robber has power but no authority. Whereas authority is the power to enforce law and take command, and to expect obedience from those without authority. Authority can exist with or without power, for example a teacher has authority over the pupils but no real power. Steven Lukes states that there is three dimensions of power, decision, non decision making and manipulating desires. In parliament when a law is being discussed by MP's and any other form of political group there must be a body which has power so that they can actually come to a decision.
Authority is basically the right to do something whereas power is the ability to do it or get it done, it can be said that authority is a form of legitimate power (CIMA,2010 Entreprise Management)
Authority is the ability to exercise power for enforcement. Power is the actual wielding of the authority.