The Mirror used the same quote attributed to New! magazine (Whatever the hell that is) in the original MSN notice. The other articles today sloppily reported that Stevens made this statement to The Mirror directly. What I find most interesting is that The Mirror adds the following bit of information that was not in the MSN piece, "The singer has a final audition to win the part of Gwen opposite John Barrowman's Captain Jack in the post-watershed sci-fi show."
Now last I had checked, Gwen was just a name that RTD had casually thrown out in the context of Torchwood in this month's Doctor Who Magazine. That "Gwen" is in fact a major character in the show, or Captain Jack's partner is far from official. So, either The Mirror has some inside information, or they are getting their news from forums and blogs like this one which have jumped to that same conclusion. Way to go guys! Good work, let's see how many more rumours we can get started!