Well you can't - bet on it that is. Bookmakers have suspended betting on the new Doctor on the grounds that they've heard that the role has already been offered to Rory Kinnear, though he hasn't accepted yet.
Might all be a reaction to a well-placed rumour and odds open again tomorrow.
We could do with another Rory in the TARDIS, mind you.
First reaction from Mark Gatiss on the news: "I can confirm that Rory Kinnear will be the new Doctor - and I should know because I'll be playing him!" Allegedly...