I'm getting pretty much exactly the same symptoms, I'm from Leeds LS27 (ex C&W) area. I've tried different NIC's, with and without firewall/router, unplugging cablemodem and leaving for 10 mins etc.
One peculiar problem I've noticed is that
http://192.168.100.1/ for cablemodem and a similar page for my router also sometimes fail to load or load very slowly.
The only things I can think that have changed on my pc recently are a driver for my NIC via Window's Update (which is why i tried a different NIC) and the virgin media webproxy removal.
If anyone has any insight into this I'd be very much appreciative.