Powell v Moody, whilst never having been technically overruled, is a case which has very limited use, is limited to its particular facts and is arguably completely out of date.
It involved a motorcycle going down the outside of a tanker on the wrong side of the road past a junction. Insurers rely on it because it was a great victory for them and it seems that few solicitors have actually read the case report properly. There have been subsequent decisions undermining this case, but the insurers always seem to forget about them.
See our detailed FAQ on Filtering and Powell v Moody