But that doesn't mean there has to be a connection between them. You know how many Thomas O'Briens I've met in my life, including my Dad (and then there's my Grand-dad, but he died before my parents even met)? That's why I go by my initials to create "Toby". And even then I've stumbled across at least a few others by that name!
Besides, I'm still not convinced that Dr. Owen Harper of 'Torchwood' is even human.
This suspicion was initially raised by the unique bone structure to the actor Burn Gorman's face. I was kind of hoping he'd turn out to be.... well, not alien, but perhaps an evolutionary side-step for humanity from some parallel dimension.
And then that strange sneer he gave to the Weevil in the episode "Combat" convinced me that there was something... "other" about him.
Even so, if he does turn out to be human, he's Welsh and the one from the sitcom played by Eddie McLintock is American. I wouldn't be surprised if you had to go back many generations to find a common ancestor, and what would be the point?
Had there been a genetic similarity due to casting, now that would have been a different story!
However, he still could be related to an Owen Harper who was played by Christopher Llewellyn in an episode of 'The Bill' ("474") this year......