David Tennant; departing Doctor WhoNovember's Doctor Who special, The Waters Of Mars, marks the beginning of the end for 10th Doctor David Tennant, as he's set to leave the Tardis for good.

We caught up with him and show boss Russell T Davies, to get a few hints on the Doctor's final battle.

The Waters Of Mars sees the Doctor team up with feisty Captain Adelaide Brooke (Lindsay Duncan) to fight a terrifying threat.

Do you think The Waters Of Mars is one of the scariest episodes you've done?
Russell: Is that one of the scariest?
David: Probably. It tells a different sort of story I think, it's a long time into the episode before the Doctor takes control and I think that's what's unnerving about it. It's not the standard structure. We expect the Doctor to know how he's going to win through - and he sort of doesn't. And even though he wins in the end, it's a bitter-sweet victory. And that's part of the story we have to tell to go where we're going.
Russell: It's not scary, it's intense.

Are you still aiming the series at children?
Russell: Yes, absolutely. Have you read a Harry Potter book? I think kids would laugh at those worries, it's mums and dads people are worried about. Seriously. It's a very complicated story, frankly it's very intelligent. I think it's fantastic television for children. In fact, if any of 'em don't watch I'll slap them.

Is it any indication of where things might be going in the future?
David: I think this gives you a bit of a hint. The Ood comes to summon the Doctor. The Doctor now knows incontrovertibly that he's running from his own demise, which is a kind of lead to the final story I suppose.
Russell: All his chickens are coming home to roost. Davros warned him at the end of the last series. He's been traveling round without a companion and this story shows why he travels with a human companion, that's the point of the story. When he's alone, he gets lost in his own head and goes too far.

Which companions are returning for the final episodes?
David: Catherine Tate as Donna and Bernard Cribbins as Wilf. John Simm as the Master, not really a companion but...
Russell: The Master's wife is back too - Alexandra Moen as Lucy Saxon - suffering as ever. And the Ood.
David: There's a new Ood with a big head.
Russell: That's his name. The Ood with the big head.

Have you achieved everything you wanted to do with the series?
Russell: When I started I never imagined we could go so far with it - to do episodes with Peter Kay, or bring Davros back. I'm more than happy.
David: I got to do so much more than I ever thought I would just playing the part, let alone working with so many incredible actors. Hanging off things, being blown up, wearing make-up of myself as a 9000million year old man. It was just an incredible, continually surprising trip and I wouldn't have it any other way.

Do you feel that you've wrapped it up satisfyingly?
Russell: Oh, it's magnificent!
David: It feels like we tell a big end of an era story, at the same time handing it on which I think is important in this show which has, let's face it, been going a long time before we showed up and will carry on into the far distant future. We tell a big old farewell story and then hand it over in rude health.

What was your last day like?
David: My last day was actually on The Sarah Jane Adventures. The last line I said as the Doctor was "you two: with me, spit spot" so it was robbed of any epic quality! It was very emotional saying cheerio. There's lots of scenes in the final episode that were very sad to play. I think if one of them had co-incided with the actual final day I would have been a bit of a puddle. As it was I kept a mildly stiff upper lip.

Did either of you keep any souvenirs from the set?
David: You really aren't allowed. People think you can just walk away with a box full of stuff, but the license fee is very well protected, as it should be! I did get a little gift box at the end - of stuff they didn't need any more! I have my own sonic screwdriver. I think there's a new sonic screwdriver now...
Russell: I wouldn't know.
David: Neither do I, but so I'm told.

Do you feel any regret when you see pictures of the new Doctor Who series being filmed?
Russell: I'm straight on 'em.
David: It's weird, I remember thinking that would probably happen, that we'd start seeing snaps of them, and I was nervous about how I'd feel. I'm thrilled that it's carrying on but of course you feel a little bit proprietorial. But I've just been very excited to see what's going on. I just can't wait to see it. I remember what it felt like to be where Matt is now, it's really exciting to see someone else starting out on that journey.
Russell: It's funny, because when you're on the inside and you see those spoilers you think it's dreadful. But on the outside - it's exciting!

Russell, is it true that you're pitching an American version of Doctor Who to US networks?
Russell: Absolutely not. On my dead mother's life.

What are you doing?
Russell: Developing things. New things. I'm not going to tell you what they are because they'll probably never exist. There's a recession out there. We'll see. American Doctor Who... I'll write that down.
David: I'll do that, I can do the accent.
Russell: There we are! Oh... we shouldn't have done that.
David: (loudly) That was a joke! Don't print that!

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