A simple but reliable poloidal beta response model is derived from Goldston's scaling law and successfully applied to a large number of plasma configurations and pulses in the JET tokamak. It provides a good prediction of both transient phase and steady state conditions without the need of an auxiliary pulse. The model, although non linear as a function of the input power, is actually linear if the input quantity is the square root of the overall input power divided by the plasma current. The model can then be used for the design of an integrated feedback controller that simultaneously regulates plasma current, position, shape and poloidal beta.