Now, I live in Scotland, so yeah, it is very often overcast, and when a big yellow dot appears in the sky we wonder for a moment what it is. :) But what I'm looking for is some kind of actual explainable phenomenon that would cause this regularly/consistently.
I'm not really picky about what causes it, at least not at the moment, because the background is pretty fluid and I can adapt the backstory to particles in the atmosphere (because of something catastrophic happening elsewhere - IIRC fallout from Chernobyl affected sheep in Wales, that sort of thing) or something screwy involving global warming and the Gulf Stream or whatever. Given the location, I'm not entirely sure I can get away with volcanic ash! But if Iceland blows up and it works, I'll take it. :) Pollution could quite possibly be a good source - if the energy supplies have been mostly knocked back to coal, might I be able to claim the sorts of dense fogs that the nineteenth-century used to have? (Peasouper/London particulars?)
I'm not yet sure about the duration I need. The longer the better.
Googled variants on post-apocalyptic/effects/gray/dark/hazy/o