A novel concept for directly quantifying the value of frequency regulation services of individual generators is proposed in this paper. Individual generator dynamics are explicitly incorporated into the optimisation problem as constraints, which allowed the frequency fluctuations to be also directly monitored and controlled. The approach eliminates the need for not well defined concepts of primary and secondary responses. The developed optimisation problem contains a mix of algebraic and differential equations. In order to solve this complex problem, generating plant dynamic equations are transformed into discrete equations and then a Benders based decomposition applied. The validity of approach is demonstrated on an example with 8 generators.