I think it's less inflation and more opportunism. A £100 increase is mega. I've noticed perhaps a roughly ten percent increase in the last two years in average wg cost which is about in line with inflation.
The issue is they seem to all share a set pricing. 100, 120, 140, 180, 200, 220, 250, 300, 350, 400, 500. It's non linear and when they bump their price it can sometimes mean a 25% increase.