I found this out too, had 4 pairs of Grensons and they all lacked any structure and went misshapen after a while, the sole in front of the heel dropped as the shank inside was not substantial enough to support it.
I now wear Trickers country range for everyday wear (boots and shoes) and for smarter wear George Cleverly RTW (made on their lasts by Crockett and Jones) and the quality is miles ahead of Grenson,Barker,Loake etc.
Grenson are all hype but little substance.