A new swarm optimisation algorithm, that is, fruit fly optimisation algorithm is proposed to tuned several classical controllers for multi-area multi-source interconnected power system under deregulated environment. In deregulated environment, for multi-source combination of reheat thermal, hydro and nuclear generating units in each control area with appropriate generation rate constraint and AC/DC link. The performance of several controller such as integral (I), proportional-integral, proportional-integral-derivative, integral-double derivative (IDD) and proportional-integral-double derivative (PIDD) are compared under different power system scenario and it is found that PIDD controller performs better than other controllers. Then sensitivity analysis is performed with system parameter variation from their nominal values. Sensitivity analysis reveals that optimum gains of PIDD controller need not be reset for wide variation in system parameters.