British actress Michelle Ryan, who played the lead in the short-lived revival of Bionic Woman, will not become a regular star of Doctor Who, even though she plays the Doctor's companion in his latest adventure Planet of the Dead.

Planet of the Dead is one of four Doctor Who specials that will air in Britain between now and next year. David Tennant plays The Doctor in these episodes. Michelle Ryan co-stars in Planet of the Dead as Lady Christina de Souza, a character who shares the Doctor's adventure. However, she told the British tabloid The Sun that this does not mean she will now be by the Doctor's side on a regular basis.

"Please don't put your bets on me being the next assistant," she is quoted as saying. "You would be wasting your time. Doctor Who is amazing but I think people presume, 'Why wouldn't I want to do it as a regular thing?' I'm a commitment-phobe."

Ryan's face became familiar to British television audiences in the BBC soap opera EastEnders and later went on to land roles in Jekyll, Merlin and NBC's Bionic Woman remake.

In other Doctor Who news, Tennant admitted recently that he had to rediscover the series' titular character when he began filming Planet of the Dead. In the months before filming began Tennant had been immersed in the character of Shakespeare's Hamlet.

"At the read-through for Planet Of The Dead, I found it quite tricky to get into the mindset," he is quoted as saying by The Sun. "Coming back this year, for these specials, felt a bit like returning to the day job after a summer holiday. Getting on set, putting on the costume and being surrounded by everyone, is like slipping back into something very familiar. It’s like coming home."

Tennant will be replaced as the Doctor by the relatively unknown 26-year old actor Matt Smith. Smith's appointment was supported this week by former Doctor Who star Freema Agyeman, who played a former companion of the Tennant's Doctor, Martha Jones.

"He's great," Agyeman told the website Digital Spy. "I can imagine there must have been a fair few people up for that role and for the producers to have such confidence in him, he must clearly have blown them away. He looks absolutely fantastic. He's a really good actor in all the other things he's done. I think he's going to be outstanding."

Agyeman also played Jones on the Doctor Who spinoff Torchwood and is currently appearing in Law and Order: UK.

Doctor Who: Planet of the Dead premieres in Britain on the BBC on April 11. Episodes of Doctor Who have aired in the United States on SCI FI Channel and BBC Worldwide and in Canada on CBC and Space.