[Terry, who as he says himself was “there at the beginning”:][link]
>The unexpected, unadvertised solution which kisses it all better is known as a deus ex machina – literally, a god from the machine. And a god from the machine is what the Doctor now is. A decent detective story provides you with enough tantalising information to allow you to make a stab at a solution before the famous detective struts his stuff in the library. Doctor Who replaces this with speed, fast talking, and what appears to be that wonderful element “makeitupasyougalongeum”.
[link]: http://www.sfx.co.uk/2010/05/03/guest-blog-terry-pratchett-on-doctor-who/ “GUEST BLOG Terry Pratchett on Doctor Who”