I’ve never actually written a script where I didn’t know who the Doctor was going to be. You just start thinking about the actor’s voice, speech patterns, mannerisms, and the whole attitude.
– Mark Gatiss

Original article, ‘Sherlock’s Mark Gatiss on writing for Doctor Who’: http://www.vulture.com/2014/09/mark-gatiss-interview-doctor-who-robin-hood.html
On adapting Sherlock Holmes: http://www.digitalspy.co.uk/tv/s129/sherlock/interviews/a358335/sherlock-mark-gatiss-qa-horror-is-a-big-part-of-sherlock-holmes.html#ixzz3ZXc5W6zA
On the struggle for the crown: http://www.theguardian.com/tv-and-radio/2015/may/01/mark-gatiss-doctor-who-is-my-first-love-baftas-2015-television