This is not an FMV or fan edit, this entire thing is an unexpectedly moving scene from one of the goofier episodes of the new Dr. Who.
I've always loved this hymn, I've always thought it was beautiful, but I suspect this probably played out considerably more emotionally in the UK than in the 'States. (Most Americans I know felt the scene either dragged on, or was entirely inappropriate because "There won't be religion in space." I never really understood that kind of thinking) Back during World War II, during the Battle for Brittain, and in the closing days of the war, when the V2s were coming in, the population used to ride out the attacks in the city's sprawling subway tunnels.
This was apparently a pretty terrifying ordeal: rumblings and shakings from above, the power frequently went out, leaving you with nothing but subterranean blackness, crying babies, and panicky idiots all around, and of course the frightening noises from above; sometimes the tunnels would collapse and kill people.
In order to keep people's spirits up, and calm them down, there were song leaders who would encourage people in the tunnels to keep singing, concentrating on that, rather than the fact that they could die at any minute. They sang pretty much anything, "God Save The King," and popular songs, but of course given the circumstances, people tended to gravitate towards hymns, and this one was one of the most popular.
So I think, being a part of the British Conciousness, this is the kind of thing that immediately connects with them and punches them in the gut, whereas, over here in Fortress America, we can't really begin to understand it.