Trainspotting's Robert Carlyle is set to take over from David Tennant as the TV time traveller Doctor Who.

Fans of the Doctor are speculating that Tennant will quit the cult BBC show before filming of the fifth series begins in 2009.

Bookmaker William Hill is offering 2-1 odds that fellow scott Carlyle will become the 11th Time Lord when The Doctor next regenerates.

Speaking to the Telegraph a spokesman for William Hill said: "We get lots of calls from Dr Who enthusiasts who want to put bets on the next Time Lord. Robert Carlyle is currently the favourite but it changes all the time."

Other hot tips to play the Doctor include Jason Stracham, Alan Davies and James Nesbitt.

Excitement over the next Doctor will reach fever pitch as the current fourth series reaches a climax this Saturday. The BBC are keeping the ending under wraps with no preview tapes allowed to be made by production staff.

Although Tennant has refused to confirm whether he will be quitting his role as the Time Lord, tough guy Carlyle hasn't ruled out stepping into his place. He says, "Would I do it? Possibly."