Capaldi recently announced he would be stepping down as the 12th TV Time Lord at the end of this year (17), prompting speculation about his successor.

And following former Doctor Who sidekick Billie Piper's call for the next man to be a woman, it appears bookies are getting serious about a sex change.

Early frontrunners included The Night Manager star Olivia Colman, Ben Whishaw and Rory Kinnear, but now Michael Clayton's Tilda has jumped out in front in the race to find a new Doctor.

Ladbrokes have slashed her odds to 7/2 after a rush of bets, putting Tilda ahead of Colman and Whishaw as the favourite to pick up the keys to the Tardis from Capaldi, who will make his final appearance as Doctor Who in this year's (17) Christmas episode.

And Swinton has a very important fan backing her as the next Doctor Who - former Time Lord Paul MCGann, who tweeted a photo of the actress in clown makeup and wrote: "Imagine Capaldi regenerating into..."

Meanwhile, the sci-fi show's outgoing executive producer, Steven Moffat, is also behind the idea of Doctor Who becoming a woman for the first time.

"I think the next time might be a female Doctor," he said last year (16). "I don't see why not."

Another former Doctor Who actor, Matt Smith, is also reportedly interested in reprising the role, and comedian Richard Ayoade is also considered one of the favourites.

Announcing his decision to step down during a BBC radio interview last month (Jan17), Capaldi said, "I feel it's time to move on... This'll be the end for me. I feel sad. I love Doctor Who. It's a fantastic programme to work on. I've never worked the same job for three years... It's been cosmic."