  We compute the combined two and three loop order correction to the spin-spin
correlation functions for the 2D Ising and q-states Potts model with random
bonds at the critical point. The procedure employed is the renormalisation
group approach for the perturbation series around the conformal field theories
representing the pure models. We obtain corrections for the correlations
functions which produce crossover in the amplitude but don't change the
critical exponent in the case of the Ising model and which produce a shift in
the critical exponent, due to randomness, in the case of the Potts model.
Comparison with numerical data is discussed briefly.
