Alright, so I've been giving this a bit of thought. Not really about places which are likely to have large surviving populations, but places that might have kinda cool survivor societies, specifically the Isle of Man, although the likelihood of it surviving is pretty slim. It can be easily reached by ferry, is right next to England (which I think consensus agrees will go, and go fast), and relies on tourism for its economy. Really, it's only saving graces are that the population is mostly contained in large towns on the east coast, and the high hills of the interior might act as a temporary obstacle to any creature once on shore. Really though, this is just me indulging myself in hypothesising.
So the Isle of Man sits in the middle of the Irish Sea between Great Britain and Ireland. Since the Manx are in the middle, they act as a sort of trading hub for the other survivor nations around the Irish Sea, as they still have the Steam Packet ferries to ship things about. The fuel for them would probably some terrible combination of oil extracted from peat and distilled alcohol that fouls up the engines terribly and requires them be cleaned out after every other voyage. The Manx are thus relatively wealthy and powerful in the region (although still woefully under-armed and under-equipped by the standards of any of the Nordic countries).
The island is governed by the Tynwald parliament, and has been since the UK government collapsed in their Year 0. It consists of the elected House of Keys and the executive Legislative Council, which meet at Tynwald hill for ceremonial purposes, or the new Parliament building in Castletown for general business, organising the running of the island (peat conservation, land disputes, trade disputes etc.), as well as operations in which Manx cleansers support the efforts of survivor societies in Great Britain and Ireland.
For religion, worship tends to be towards Manannan Mac Lyr, the old sea-god who protects Man. There are a few dedicated priests who claim special connection of him, but mostly he is invoked in prayer by anyone in need. Other older Celtic gods and figures appear in mythology, but Manannan is the patron of Man.
Infection is controlled by an internal police force, an institution descended from the original tiny military garrison put in place after quarantine was declared. It uses Manx cats bred and trained to Nordic standards, although other breeds are introduced to keep bloodlines relatively diverse and to prevent the cats from being woefully inbred. Infected Beasts aren't distinguished by size on Man since few ever get bigger than trolls, so are generically called "bugganes", which also applies to cetacean Beasts (i.e., whales, dolphins etc.).
Since it has limited arable land, sheep and goat farming is the main form of agriculture. Fishing is possible, but there are often disputes between fishermen from Man and other survivor societies around the Irish Sea. Man therefore requires imports of food from those survivor societies elsewhere: Scots-Gaelic forester communities in Galloway, Welsh-speaking sheep farmers in Snowdonia, arable farmers in Northern Ireland, and the English-speaking Muslim and Sikh salvage communities in Lancashire. In return, Man exports wool for clothing, peat for fuel, and its cleansers, since it has men and resources to spare.
Like I said, it's not likely, but I think it would be pretty neat.