Doctor Who: Runners and riders

Speculation is mounting over who will replace David Tennant as Doctor Who, with an announcement due on Saturday.

The 37-year-old star announced he would no longer play the Time Lord after a number of specials.

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

PATERSON JOSEPH

Joseph is the bookmakers' favourite to succeed Tennant

The actor is the bookmakers' favourite to succeed Tennant.

If he lands the part, the 44-year-old will become the first ever black doctor.

The star has already appeared in two episodes of the show playing Roderick alongside previous doctor, Christopher Eccleston.

He is a popular comic actor and has appeared in Peep Show, Jekyll and Green Wing.

DAVID MORRISSEY

Morrissey starred in the much-derided Basic Instinct 2

Already appearing as a character called the other Doctor in the show's Christmas special, The Next Doctor, Morrissey is another favourite to win the part.

In 2003 the 44-year-old was nominated for a Bafta award for his starring role in political drama State of Play.

More recently he appeared with Natalie Portman and Scarlett Johansson in the Hollywood film The Other Boleyn Girl.

SEAN PERTWEE

Sean Pertwee is reportedly eager to follow in his father's footsteps

Ignored by the bookmakers, but a strong contender according to Doctor Who fansites, the 43-year-old actor could follow in his father's footsteps.

Jon Pertwee, who also played Worzel Gummidge, was the third Doctor from 1970-1974, before Tom Baker took over the role.

The Event Horizon star has revealed he would be interested in appearing in the show, according to reports.

JAMES NESBITT

Nesbitt first came to popular attention in the Cold Feet series

The former Cold Feet star is another high-profile star favoured by the bookmakers.

The 43-year-old actor, born in Northern Ireland, has starred in a long list of TV dramas, including Murphy's Law, Jekyll and The Passion.

However Nesbitt has told BBC News he is not interested in the role.

RUSSELL TOVEY

Russell Tovey is the first choice of Doctor Who writer Russell T Davies

Last year the actor appeared as Midshipman Frame in the Doctor Who Christmas episode, Voyage of the Damned.

The 27-year-old, who appeared in The History Boys and Gavin and Stacey, is the youngest contender believed to be under consideration.

In September, Doctor Who writer Russell Davies suggested Tovey should be Tennant's successor.

The creator, who leaves the show next year as lead writer and executive producer, said he thought Tovey was "going to be huge" and is "amazing".

JAMES McAVOY

McAvoy won the Bafta Rising Star Award in 2006

The star has begun to build a successful film career in Hollywood.

He has landed starring roles in the Oscar-winning movies Atonement, The Last King of Scotland and The Chronicles of Narnia.

The 29-year-old is married to his former Shameless co star Anne-Marie Duff.

MATT SMITH

Matt Smith has been making his name in plays in theatres in London

Smith appeared in Alan Bennett's play The History Boys at the National Theatre in London, and alongside Christian Slater in Swimming with Sharks in the West End.

Two of the productions in which he featured - That Face and On the Shore of the Wide World - won Laurence Olivier Awards.

The 26-year-old's teenage plans to be a footballer were scuppered by a back injury so he studied drama and creative writing at university.

His TV appearances have included the BBC's versions of The Ruby in the Smoke and The Shadow in the North, both of which featured Billie Piper.

CATHERINE ZETA JONES

Zeta Jones shares her Welsh roots with writer Russell T Davies

The Welsh actress-turned-Hollywood-star is creator Russell T Davies's pick for the first female Doctor Who.

"I wouldn't be against the idea of having a female Doctor. Catherine Zeta Jones would be great," said the writer shortly before Christmas.

The 39-year-old, who currently lives in the US with husband Michael Douglas and their two children, shares Davies's Welsh connections - and might welcome the opportunity to return to Cardiff where the series is made.

Nor is her versatility in any doubt. She made her Hollywood breakthrough in swashbuckling romance The Mask of Zorro and won an Oscar playing Velma Kelly in the film version of the musical Chicago.

Other notable film roles include Coen brothers' comedy Intolerable Cruelty, Entrapment and Traffic.

CHIWETEL EJIOFOR

Ejiofor won a Golden Globe nomination for TV's Tsunami: The Aftermath

Known to his friends as 'Chewy', this talented British star is another contender to be the first black Doctor Who.

The actor has successfully embraced television, film and theatre - coming to public attention with his role in Stephen Frears' Dirty Pretty Things in 2002.

Notable performances followed in Love Actually, Kinky Boots and the title role in Othello at London's Donmar Warehouse theatre last year.

He will next be seen playing former South African president Thabo Mbeki in the forthcoming Endgame.

BILLIE PIPER

Piper gave birth to a boy, named Winston James Fox, in October

Piper gained fame as a teenager when her 1998 single Because We Want To went to number one, and she went on to marry TV and radio personality Chris Evans.

Her acting career began with a part in BBC period drama The Canterbury Tales in 2003.

Doctor Who fans know her already, from her stint as the Doctor's companion, Rose Tyler, in 2005.

The 26-year-old went on to star in ITV2's Secret Diary of a Call Girl and married her second husband, Laurence Fox, on New Year's Eve 2007.