Image caption Will Peter Capaldi, Billie Piper or Chiwetel Ejiofor be the next owner of the Tardis key?

Speculation is mounting over who will replace Matt Smith in Doctor Who, with the announcement due on Sunday.

Smith, who has played the Time Lord since 2010, announced in June that he would be leaving in this year's Christmas special.

The past few weeks has seen a flurry of newspaper stories guessing at who might take over in the Tardis.

Early favourites included Harry Potter star Rupert Grint and Being Human actors Russell Tovey and Damien Molony.

As in previous years, some have suggested the role may go to a black actor, with Luther star Idris Elba, Homeland's David Harewood and former rapper Ashley Walters among those mentioned.

There have also been calls for a female Doctor, with Billie Piper, Olivia Colman and Dame Helen Mirren on some wish lists.

Here are some of the names appearing in the bookmakers' lists of favourites.

Peter Capaldi

Peter Capaldi has become the late favourite to take over the role of the Time Lord from Matt Smith.

The Scots actor, best known as foul-mouthed Malcolm Tucker in The Thick of It, is 6/4 favourite, according to bookmaker William Hill on Friday. Paddy Power has him at 7/4 favourite and Labrokes 11/8.

Capaldi played Roman merchant Caecilius in 2008 Doctor Who adventure The Fires of Pompeii.

At 55, as Metro points out, Capaldi is the same age as William Hartnell when he was cast in the role as the first Doctor in 1963.

Ben Daniels

Midlands-born Ben Daniels has enjoyed a long career in TV and film and on stage.

The 49-year-old actor will be familiar to many through his role as Finn Bevan in BBC series Cutting It (2002-2005). Other TV appearances include political thriller The State Within (2006) and ITV drama Law & Order: UK.

Daniels won an Laurence Olivier Award in 2001 for his performance in the Arthur Miller play All My Sons.

Ladbrokes and Paddy Power give him odds of 4/1, and William Hill 5/1.

Chiwetel Ejiofor

Chiwetel Ejiofor's career has successfully embraced television, film and theatre.

Speaking on the The Andrew Marr Show in 2011 he said he would be interested in the role of the Time Lord if it was offered.

Coming to public attention with his role in Stephen Frears' Dirty Pretty Things in 2002, film roles have included Kinky Boots, Children of Men and American Gangster.

Notable TV roles include The Shadow Line and Dancing on the Edge.

Ejiofor is currently appearing on stage in A Season In The Congo at London's Young Vic. He won a Laurence Olivier Award for best actor as Othello in 2008.

Paddy Power has the 36-year-old actor at 12/1.

Idris Elba

Idris Elba, star of TV detective series Luther, has said he's "proud" that people have linked him with roles such as Doctor Who and James Bond.

He told Newsbeat in July the roles were "national treasures".

But the 40-year-old Londoner, who shot to fame as drug lord Stringer Bell in HBO's The Wire, has also said of the idea of playing the Doctor: "I'd look silly in a bow tie."

Elba portrays Nelson Mandela in the forthcoming film Mandela: Long Walk to Freedom. Other recent movie roles include Prometheus and Pacific Rim.

Ladbrokes lists Elba at 12/1 while Paddy Power puts him at 25/1.

David Harewood

Homeland star David Harewood appeared in Doctor Who as Joshua Naismith in David Tennant's final two-part story The End of Time (2009-10).

Speaking about being linked with the Doctor role, the 47-year-old actor told Entertainment Weekly: "It's only rumours but it's amazing to be attached to such an iconic role.

"It would be extraordinary if the BBC were to make me the first black Doctor Who, it would be extraordinary. But I'm almost scared to make any comment whatsoever."

Harewood was appointed an MBE for services to drama in 2011.

Ladbrokes has the actor at 10/1, while William Hill has 14/1 and Paddy Power 16/1.

Rory Kinnear

Rory Kinnear was tipped as an early favourite to replace Matt Smith in the Tardis, but has since ruled himself out of the race.

"I haven't been and I am totally certain that I will not be asked to be the next Doctor Who," he told The Independent in July. On Friday, Paddy Power had Kinnear as its third favourite at 6/1.

His best-known big screen role is as MI6 officer Bill Tanner in the recent Bond films. On TV he is in BBC comedy Count Arthur Strong and imminent Channel 4 drama Southcliffe.

Kinnear won rave reviews for his Iago (opposite Adrian Lester's Othello) at the National Theatre earlier this year. He has also written his first play, The Herd, which opens at London's Bush Theatre in September.

Billie Piper

Billie Piper is returning for this November's 50th anniversary Doctor Who special.

She played Rose alongside both Christopher Eccleston and David Tennant's Doctors.

Piper gained fame as a teenager when her 1998 single Because We Want To went to number one. Her acting career began with a part in BBC period drama The Canterbury Tales in 2003.

She went on to star in ITV2's Secret Diary of a Call Girl and the BBC adaptation of Philip Pullman's The Ruby in the Smoke.

Piper's most recent stage role was in Lucy Prebble's clinical drugs trial drama The Effect at the National Theatre, for which she earned an Olivier nomination.

Piper is something of an outsider with the bookies. Paddy Power puts her at 33/1.

Daniel Rigby

Daniel Rigby, according to Ladbrokes, is the biggest mover and shaker in the betting, having been 20/1 a few days ago and now standing at 5/2.

Rigby won a Bafta TV award in 2011 for his pitch-perfect portrayal of comedy legend Eric Morecambe in BBC Four biopic Eric and Ernie - beating off competition from Matt Smith (for Doctor Who) and Benedict Cumberbatch (Sherlock).

The 30-year-old actor's stage work includes the hit play One Man, Two Guvnors, alongside James Corden, in the West End and on Broadway.

Andrew Scott

Andrew Scott won a Bafta in 2012 for his role as Jim Moriarty in BBC series Sherlock.

The Dublin-born actor told website Flicks and the City in June that it was "flattering" to be mentioned as a potential Doctor.

"One has to wait to be asked," he said. "I know Mr Moffat very well, so he'll keep his cards close to his chest."

Scott, whose stage work includes Emperor and Galilean at the National Theatre, is given 8/1 odds by Paddy Power and 10/1 from William Hill.

Ben Whishaw

Rory Kinnear's fellow Bond actor Ben Whishaw, who played Q in Skyfall, is 6/1 according to Ladbrokes, while William Hill has him at 12/1.

Whishaw has also ruled himself out of becoming the next Doctor, telling the Daily Mail: "It's not going to be me. But I don't mind - I don't think you can be Q and Doctor Who. It would be a bit wrong."

Whishaw, who appeared in BBC drama The Hour, was last seen onstage opposite Judi Dench in Peter and Alice at the Noel Coward theatre.

He has just been announced in the cast of a West End revival of Jez Butterworth's Mojo, which will begin at the Harold Pinter Theatre in October.

Doctor Who Live: The Next Doctor, is on BBC One at 7pm on 4 August.