I find this movie all kinds of awesome, but it's not really a characteristic vampire movie. For one thing, there's not really any blood. The "vampires" don't really do the blood thing; they suck the, well, lifeforce out of people, kind of like J.K. Rowling's dementors. Only way sexier and more naked.
The movie starts a bit like Alien - there's something strange out there (in this case a giant shaft of a spacecraft that opens up like an umbrella) and people go and check it out. They find a bunch of batlike creatures who have apparently been dead a while, but they also find three caskets seemingly made of glass and containing three naked humanoid creatures.
The female awakens and takes the lifeforce of one of the officers, and soon the whole ship is zombified, absorbing each other's lifeforce and allowing the naked vampires to collect the energy on the ship where they were found. (Mad props to the makeup and effects people, by the way, for some pretty awesome zombie-like creature effects.) I should clarify that the whole ship is zombified save one person - Col. Tom Carlson (Steve Railsback). Carlson has a psychic link with the female vampire and has become infatuated with her, but not wanting Earth to suffer the same fate as his ship, he sets fire to the ship with the vampires still on it and gets the heck out of Dodge via the escape pod.
Sadly, this does not stop the vampires from arriving in London and causing all kinds of chaos and plaguey-ness with their lifeforce-sucking ways. Soon, martial law is declared in an effort to keep the plague contained in London. Carlson teams up with someone from the SAS, Col. Colin Caine (Equus's Peter Firth, who bless him is one of the several decent actors in this film who spends much of his screen time wearing a "what the crapping crap?!?!?!" expression), and the two of them try to stop the vampocalypse.
Oh, and it turns out that all the vampire legends we know and love started when these naked vamps came to earth that other time, a long long time ago.
The finale defies description. Here is the best I can do. Carlson and Caine find vampire chick in a church, and she and Carlson get (wait for it) naked and engage in the least sexy naked kissing I have ever seen. Carlson then sacrifices himself by impaling himself and the girl in a kind of naked-ke-bob, before the church explodes (from the sheer absurdity, I guess) and they're both sucked up into the spaceship. The end.
There's not much this story has in common with traditional vampire stories. No stake through the heart or aversion to sunlight. In fact, literally the only way to kill one of these creatures is by impaling them with lead, not a wooden stake. There are a lot more sci-fi type effects here than blood, and it looks like this movie single-handedly kept Spencer Gifts in business, because half of the lighting effects resemble those plasma globes. That's not a criticism, because it all looks rather awesome. But it's 80s awesome, if you take my meaning.
Anyway, it's still a lot of fun (though it's longer than it needs to be). Occasionally genuinely scary, even more occasionally hysterical, and naked with disturbing frequency. There's also a pretty cool score by Henry Mancini (of "Pink Panther," "Moon River," and "Peter Gunn" fame).
Check out the super-crazy finale, embedded below, if you dare. Um, I mentioned the nakedness, right? Okay you've been warned.