James Corden appears in 2 episodes with The Doctor in Modern day London without the Doctor's companions. In the first episode, the Doctor becomes the flat mate who assists James when an unknown alien takes up residence above. The 2nd appearance James has a new baby who, as he repeatedly says "only cries when I hold him." This is the same phrase he repeats at least twice to his wife while playing the baker in Into the Woods.
The director, Richard Senior, states that they're showing a TARDIS materializing inside of a Tardis and that in 40 Years of Doctor Who it's never been done, so he feels he's making "history". Actually, it's been done at least two other times: in the Jon Pertwee Adventure, "The Time Monster", where the Doctor and the Master materialize their tardises several times inside each others. It was probably best done in "Logopolus", a Tom Baker episode when the Tardis materializes multiple times inside itself.