  We reformulate the BRST quantisation of chiral Virasoro and $W_3$ worldsheet
gravities. Our approach follows directly the classic BRST formulation of
Yang-Mills theory in employing a derivative gauge condition instead of the
conventional conformal gauge condition, supplemented by an introduction of
momenta in order to put the ghost action back into first-order form. The
consequence of these simple changes is a considerable simplification of the
BRST formulation, the evaluation of anomalies and the expression of Wess-Zumino
consistency conditions. In particular, the transformation rules of all fields
now constitute a canonical transformation generated by the BRST operator $Q$,
and we obtain in this reformulation a new result that the anomaly in the BRST
Ward identity is obtained by application of the anomalous operator $Q^2$,
calculated using operator products, to the gauge fermion.
