In Doctor Who; Flatline (Season 8, episode 8) one of the trains was marked as the A113.
This is a common enough reference in American shows given that it's something of an in-joke for those who trained at the California Institute of the Arts, A113 being the room in which first year Graphic Art students are situated.
The official BBC "Fact File" even mentions it:
One of the train’s featured in Flatline is clearly numbered A113. This designation is often featured in films created by former students of California Institute of the Arts, referring to the classroom used by graphic design and character animation students. As such, A113 has appeared (with varying degrees of subtlety!) in TV shows such as The Simpsons and Family Guy plus movies including Toy Story, Monsters University and The Hunger Games: Catching Fire.
So what (or who) is the connection between Doctor Who and Cal Arts' A113?