Christopher Eccleston will have Billie Piper as his assistant

A 45-minute episode, called Rose, has appeared three weeks before the series is expected to begin on BBC One.

Rose is the name of the character played by pop singer Billie Piper, who will be the assistant to the Doctor, played by Christopher Eccleston.

It is unclear how it came to be on the web and whether it is the final cut. The BBC was unavailable for comment.

The episode - which appears to be the series' first instalment - begins with the Doctor and Rose being chased by Autons, shop mannequins that have come to life.

Christopher Eccleston is the ninth actor to play the Doctor

It has since been resurrected for a one-off TV movie and as animated online adventures. In 2003, it was voted the show people would most like to see back on TV.

It also has been revealed that Eccleston, who appeared in Shallow Grave and Cracker, e-mailed writer and executive producer Russell T Davies to ask for the role.

"He e-mailed me and said if we were looking for a Doctor Who, he'd be interested," Mr Davies told Radio Times magazine.

"It was gobsmacking because you think he's going to be doing Hamlet all the time," he said. "Which, come to think of it, he was."

The first two episodes were written by the time Eccleston was cast, Mr Davies said.

Billie Piper has turned to acting after a pop career

Julie Gardner, head of drama at BBC Wales, which has made the series, told the magazine: "We got to Chris fast.

"Russell and I had both worked with him before - he was one of the first people who was mentioned."

Eccleston will be the ninth Time Lord to take to the Tardis when the show returns.

Eccleston has also starred in TV dramas Our Friends in the North, Hearts and Minds and Linda Green as well as films such as The Others and Gone in Sixty Seconds.