Considering it's a British show, why would it have to be someone that the US has heard of? Yes it is shown around the world, but that is no reason that you MUST know of the actor/actress. Still, considering how it has been with EVERY main companion since Rose, you will have seem him/her in the show already...thats my guess. Every single companion after Rose was in the show before they got the role.
I'll second that...he is a beast when it comes to autographs. When I got mine, I was given a virtual ticket with a number of about 2000ish. I thought he would never get to that point over the course of the day.....I got my autograph done within a couple of hours!
Not entirely sure how true that is.....considering the source. A tabloid newspaper that is only out to get views/revenue from people buying the papers. Anything said by the Sun and Mirror are to be taken with a pinch of salt in my opinion