Dark Angel is the name used by two fictional characters in Marvel UK, though they have no other relation.
Dark Angel (Shevaun Haldane), originally Hell's Angel, is a fictional superheroine from the Marvel Comics imprint Marvel UK. She first appeared in Hell's Angel #1 (July 1992); the character and the comic book were both renamed to Dark Angel with issue #6 due to legal threats from the Hells Angels biker club.
She teamed up with numerous other American heroes and anti-heroes in the process, including the X-Men (particularly Wolverine and Psylocke), Hercules, Sabretooth, Doctor Strange, the Fantastic Four and the Avengers, as well as the "soul fragments" of the deceased Nuke and Nighthawk of the Squadron Supreme. She also teamed up with and/or fought fellow Marvel UK characters Death's Head II, the Knights of Pendragon, the Warheads, Genetix, Wild Thing, and Motormouth and Killpower, and joined several of these heroes in the short-lived team called the Dark Guard.
Shevaun was one of the many superheros who gathered to fight Mys-Tech in a literal apocalyptic showdown. The organization had created a double of the earth, which would grant them absolute power over the original one. The heroes would fight their way to the core of Mys-Tech, losing dozens of their own to death and destruction. Shevaun not only had to fight, she had to maintain her wildly fluctuating and painful powers to help the cosmos on a level few of her companions understood. In the end, only a small number of heroes were left alive and even a smaller number made it to the devices that could reverse time. Sevaun joins with the group, which included Professor X, Doctor Strange, one of the Knights, Death's Head and Motormouth (the last out of pure need more than anything else) and manages to reverse time just enough so that none of the heroes died and the earth wasn't in real danger. The Counter-Earth was blocked off from Mys-Tech. Only the heroes who made it to the end actually remembered all the chaos and death that had gone on before.