  We present an extension of the corner transfer matrix renormalisation group
(CTMRG) method to O(n) invariant models, with particular interest in the
self-avoiding walk class of models (O(n=0)). The method is illustrated using an
interacting self-avoiding walk model. Based on the efficiency and versatility
when compared to other available numerical methods, we present CTMRG as the
method of choice for two-dimensional self-avoiding walk problems.
