Everyone from Cadia has a British accent, although it's not quite as ridiculous as a stereotypical British one. I'm sure you can find some fine chaps in the higher ranks of the Imperial Guard or the Inquisition. They've probably incorporated digital weapons technology (like those rings that can one-shot a Space Marine) into their monocles. He winks, and whatever he's looking at is no more.
What ho, old boy, you seem to have taken some of your assumptions as fact! Dashed thing, but there does in fact exist a Space Britain in the mythos. It's a smashing place called Praetoria, and while the unwashed masses don't like the place, any proper Praetorian gentleman should! I leave this link for your perusal, old boy. Tally ho! [link]