Press kickoff for WHO begins

Doctor Who's David Tennant showed off his new assistant as the show's executive producer confirmed there would be a fourth series.
A string of celebrities stepped out to welcome Freema Agyeman who will play the new sidekick Martha Jones in the third
series with David Tennant as the Doctor.But a question mark still looms over whether David Tennant will continue his role. Neither David nor Russell T Davies - the executive producer and one of the writers - would answer who the fourth series Doctor would be.When asked if he would return, David said: "Do you know how many times I have been asked that question? Do you know how many times I have answered it?" then he smiled.Speaking about his new assistant, he said: "The big story is Freema Agyeman is Martha Jones which is the big event of series three."Finishing one relationship is always difficult, but then you plunge right into another one, that's what I find works best."Freema said: "Billie (Piper) did a tremendous job. I know no-one likes change but the nature of the show is change and hopefully fans will be cool with that and give me a chance."There are similarities between Martha and Rose. She's not a wall flower and there is a lovely and different relationship with her and the Doctor."It's been an amazing experience. I did not know what I was auditioning for until the last minute."The fans outside were so warm and welcoming."