The Great War, It isn't known who dropped the first bomb, but that hardly matters. It lasted a very brief amount of time, but was unbelievably destructive. More energy was released in the early moments of that war than all previous conflicts combined. Most countries were heavily nuked, their entire populations obliterated by the nuclear Fallout, one was not. Britain suffered a different fate to the rest of the world.
They had reestablished that ancient rivalry with France, a country that they nuked during the Great War. France however, behaved differently. Seeking only to conquer to the country for resources (Britain had somehow managed to evade the oil crises) they unleashed upon Britain a disease that turned most of the population blind, there were a few who remained immune to its effects but their numbers were small. The date is 24 October 2077 and you are one of the last people alive in the world, stranded in a powerless country of the blind. Britain's grand secret however is also alive and growing in numbers...
Triffids
These giant walking plants were developed by the British for the high quality of their oil, they had saved the country from the worst of the oil crisis, though they are deadly and have a tendancy to attack any animals they come across. Their sting is deadly and a proper sting will kill you near instantaneously. Luckily their stingers are harmless when you are properly protected, they are however organised, stealthy and present in overwhelming numbers.
Technology
Standard Fallout fare, not quite so many readily guns around due to comparatively tight gun laws in the country...
very sorry this is taking me so long to write up lol