Need Help Finding The Name Of A Horror Movie About Cloned Serial Killers

I have been looking for the name of this movie for years. Didn't recognize any of the actors and only saw it once. I believe it's British. The story is about a guy who is being framed for murders and receives help from a woman whose sister was killed. I think her sister was killed in the same fashion as the current victims but that killer is dead.  They become romantically involved and in the end discover that he is a clone of her sister's killer. They also discover that his close friend is a clone of another serial killer who was the one framing him. A few other people they encounter are also cloned killers as part of a nature vs. nurture experiment.