Critical indices of several operators in the generalised Villain model are calculated to second order along a critical line emerging from the model's multicritical point. Relations between these expansions support the identification suggested between this line and a critical line of the Ashkin-Teller model.
Lines of critical points which emerge from the two-dimensional planar model's multicritical point are analyzed. These lines seem to be in the same universality class as both the Ashkin-Teller and the eight-vertex (8V) models' critical lines, with the multicritical point being isomorphic with the 8V model at both the points $tanh2\ensuremath{\lambda}=\frac{\sqrt{2}}{2} \mathrm{and} \ensuremath{-}1$. Expansions of critical indices about these values of $\ensuremath{\lambda}$ are performed. If this analysis is right, then this work permits the evaluation of a whole class of interesting correlation functions at the critical point of the F model and that of the four-state Potts model.