Author Gaiman wrote series six episode 'The Doctor's Wife', which went on to win the 2011 Ray Bradbury Award for 'Outstanding Dramatic Presentation' and the 2012 Hugo Award for 'Best Dramatic Presentation, Short Form'.
"For our generation you watch Withnail [And I], and that defines so much for all of us as a film. He very kindly did an impression, 'Booze. I must have booze! Give me booze!'.
"He's just a wonderful, kind, clever, brilliant actor. He's got a lovely spirit and nature and I think he's perfect for Doctor Who."
Grant's appearance is his first canonical Doctor Who performance after his voice work on animated webcast 'Scream of the Shalka' and appearance in Steven Moffat's comic sketch Doctor Who and the Curse of Fatal Death