Do the tiers reflect the infection numbers / rates of increase anyway? I doubt it.
very vaguely sort of
tiers are set at county level as its easier than more granular use of district councils...but it means a high rate of infection at the opposite end of a county means low infection areas get caught.
the political answer is: "well if you are in a county will a high infection part, it will spread out, making the low infection areas catch up" (which Id say is bolox)
