"HOLY CRAP "I knew he looked familiar! Dean Thomas, 20 points to Gryffindor!" The actor is Alfie Enoch who appeared in the Harry Potter films as Dean Thomas. He is in Sherlock season Daaaaayyyuuumm 20 points to Gryffindor indeed.
I just dreamt that I was the Doctor’s companion, and then while we were fighting daleks at the BBC studios, Benedict Cumberbatch asked if he could come with us to explore the universe. You have to stay here and finish filming season