  Using canonical quantization we find the Virasoro centre for a class of
conformally-invariant interacting Wess-Zumino-Witten theories. The theories
have a group structure similar to that of Toda theories (both abelian and
non-abelian) but the usual Toda constraints on the coupling constants are
relaxed and the theories are not necessarily integrable. The general formula
for the Virasoro centre is compared to that derived by BRST methods in the Toda
case, and helps to explain the structure of the latter.
