I'm not from the UK but from what I understand the reclassification from Class C to Class B, carries with it more severe punishments for possession and distribution, which has perhaps dissuaded dealers.
I know that in Canada, several years ago, there was a bust of 1000 kilograms of ketamine that forced many users to stop, however some of the addicts maintained, putting whatever mixture of white powders up their noses as long as it was sold to them as ketamine. After a few months things returned to normal, though I never again saw ketamine for as cheap as I did when I was first introduced to it.