The London Natural History Museum calls this insect the "urban bluebottle blowfly." Its native range is very nearly the entire Northern Hemisphere, and can also be found anywhere else on earth there are humans and dead animals. In warm climates they are most conspicuous in winter, when other flies are rare or simply less active.
I am fairly certain that badnoodles' identification of this species for me has solved the mystery of the "really big black housefly" that I've encountered in various situations. In one animal facility where I was a volunteer, a plumbing malfunction led to a build up of water contaminated with monkey feces in a basement. Big black flies, twice the size of houseflies, became a persistent presence in the facility for a few weeks; the monkeys made a sport of catching them and eating them. I hasten to add that badnoodles describes them as "strict carrion breeders," and so it may have been another fly in that instance. The blue iridescence of this species is more subtle than some other bottle flies, and in flight looks black. Orange markings on the face help distinguish it from closely related species. This individual was caught indoors, and may have been seeking a place to overwinter.
Calliphora vicina is the focus of more attention than many flies, due to its importance in forensic entomology. Depending on temperature, the development of the larva progresses at a very predictable rate. The circumstances and time of a human death can be more accurately determined by experts using the presence of this urban species.