Found it
Some what ironically was the state of the former United Kingdom, which was actually improving, the resettlement areas set up American led NATO forces before the Europe outbreak had manage to establish contact with each other and form a loose federation of communities that were dotted around England, Scotland and Wales. By early 2006, the Federation of Great Britain was proclaimed in St Andrews, Scotland, which included St Andews, the most affluent of the resettled areas, as well as the Isle of Wight, Dover, Folkstone, Portsmouth, Fort William and Angelsey. Smaller villages near these towns were later cleared of bodies and wreckage and also resettled, and rudimentary phone lines and power lines were set up or reconnected, allowing communication between the citizens of the British Federation of some 30,000 estimated people. The Federation was run by a joint civilian and military council upon its proclamation, with plans for elections in 2008.
What about this extract suggests a republican form of government? Federations are not inherently republics, and the focus on the monarch as the physical embodiment of the British nation is widespread in British culture. I sincerely doubt that the Federation of Great Britain would reject King Charles III outright - presumably a reunification of the FofGB with Northern Ireland is expected in the future.