@tootyfruitypickle
The decision to move up in tiers is not solely on cases per 100K rate.
A significant element is related to hospital capacity and admissions/covid occupancy trends in neighbouring councils
If the hospitals in neighbouring local councils are already at full covid capacity and patients are being diverted to hospitals in the next council, your council will then be put into a more precautionary lockdown to try and prevent hospitals being overwhelmed.
The following comments are merely anecdotal - information from various docs and nurses I spoke to a fortnight ago: two weeks ago Kent Medway hospitals covid beds were full, with overflow cases being sent to Maidstone Hosp. Maidstone Hosp was filling fast and Tunbridge Wells (Pembury) Hospital was bracing for Maidstone reaching capacity as they were poised to take the overflow - despite the fact that Tunbridge Wells had one of the lowest case rates in the country (which TBH IMO doesn't say much, but nonetheless). Many were furious that T Wells was in tier 3 but having spoken with NHS staff and hearing the imminent situation they faced, I truly understood why the govt had T Wells in tier 3.
The decision to move tiers encompasses a far wider range of criteria than just cases/100K rates. It's really frustrating as we don't always have access to the full extent of the data/info they are planning around.