Potential survivor communities in Britain in Year 90. I was thinking the collective population of the Isles would be between 20-50,000 survivors. That might seem like a lot but since the population of the UK was over 63 million in 2011, not to mention the 5 million in Ireland, I think this is pretty fair.
I had just been thinking about this over the weekend, though I meant to add a few areas in the Lake District in England and Northern Wales. The colours are basically the same as on Minna's map, pink being safe zones and red being areas of risk.
If no one minds I shall attempt to do a speed description of this world.
Mainland Britain was completely swamped by the number of infected but managed to establish several safe zones in the Scottish islands and highlands before the began to completely abandon the more heavily populated areas in England. Cooperation with the Irish government meant that several thousand Britons were successfully evacuated to Ireland whilst the Royal Navy prevented potentially infected ships from making landfall. The Irish government meanwhile was able to buy some time, moving large numbers of their own civilians to safe zones in the rural west of the country.
For a time it seemed like the British government would be able to survive, holding the line in Scotland and pushing south in the winter to reclaim more land. However the Irish containment was breached, a Royal Navy ship went rogue and let through several boatloads of refugees, defending them from the Irish navy's attempts to sink them before it itself was sunk by the British military. Attempts to kill or quarantine the refugees proved insubstantial with Irish military personnel becoming infected, members of the British army were brought in to help contain the outbreak in Dublin, just as the Scottish outbreak was beginning to get worse... DUH-DUH-DUH-DUUUNNNN!!!
So in Year 90 the British government survives in Stornoway, on the Isle of Lewis. It's mostly focused on the surviving royal family since it's hard to maintain a democracy when your population survives in very isolated communities and also goes through periods of rapid growth and decline (no contraceptives plus lots of famines and Rash outbreaks makes things messy). Things are sort of neo-feudal with the leaders of survivor communities making deals to work with the central government in exchange for protection. The population in Scotland has a lot of English and Lowland Scot descendants, much to annoyance of the Highland Scots who are now a minority. There's still some Scottish nationalism, but they're mostly ignored as idiots.
The surviving Irish government is under the protection of the British one, but they are very isolationist and don't trust their northern neighbours as far as they could through them since the British are blamed for the Irish outbreak. There's also a lot of infighting between Irish survivor communities, especially between those that have large English or Northern Irish populations.
I meant to add about the English and the Welsh. There's a few bases in the Lake District, they were originally small forgotten survivor communities that managed to recontact the government about 30 years after losing contact. The civilian and non-immune population were evacuated to the recently cleansed Isle of Man (the Trolls abandoned it once they ate all the livestock). The surviving Welsh communities were discovered by Irish treasure hunters in Year 86, the British government is trying to talk them into rejoining the rest of the survivor communities but nearly 100 years of isolation has left them with a great distrust of the outside world.
I'm done.