1. A method of controlling the behaviour of a plant having an input and an output by feedback, comprising the steps of: receiving an input signal; deriving a plant input signal and a simulation input signal from the input signal; applying the plant input signal to the input of the plant; deriving a plant feedback signal from an output of the plant; generating a simulated signal by simulating an aspect of an assumed behaviour of the plant in dependence on the simulation input signal; generating a difference signal by subtracting the simulated signal from the plant feedback signal; and, modifying the input signal by feedback in dependence on the difference signal, wherein the step of modifying the input signal by feedback is performed prior to the step of deriving the plant input signal and the simulation input signal from the input signal.