I made this cake twice, once for my niece (who became a fan after I forced her to watch an episode) and one for a 40th birthday. The TARDIS is made from rkt and covered in fondant; The Doctor and his companions, Amy and Rory are made from gumpaste. (One cake is raspberry swirl with lemon buttercream and the other chocolate cake with ganache.) They are almost identical, just a few tweaks to make it personal.
Nicole --- http://www.facebook.com/thecakeofit