A host of big names have joined the race to play the next Doctor Who following Matt Smith's announcement he's stepping down as the TV Time Lord later this year (13) - but series producer Steven Moffat is refusing to name names. Smith will vacate the Tardis after wrapping the show's 50th anniversary episode, which will air in November (13), handing over the keys to a new Who. Speculation about a makeover for the sci-fi show began when John Hurt was introduced as The Doctor in the most recent season finale and now fans have taken to blogs and webchats to discuss all manner of options. Hurt will return for the 50th anniversary episode, but executive producer Moffat is refusing to name Smith's successor. He says, "Somewhere out there... is someone who's about to become The Doctor." Fans seem to like the idea of a black Doctor Who, with Homeland's David Harewood and Idris Elba mentioned as potential possibles, while there's growing interest in a female taking over the lead - Dame Helen Mirren, Olivia Colman and Fiona O'Shaughnessy appears to be early frontrunners. Meanwhile, bookmakers William Hill have made former Harry Potter star Rupert Grint and Russell Tovey from Being Human their joint 10/1 favourites to be named the next Doctor.