What’s gorgeous about it is that I get to sort of confess to my imagination every day. So I get to play around in a mad, imaginary world every day, which is limitless and timeless, and endless and boundless. You know, that is as close as you get to sort of magic really, I suppose, in many ways.

“The thing is, right, I’ll take Patrick Moore, fine. But I definitely haven’t got an underwear model’s body, no way, not on this schedule. All my gym’s gone out the window. God no, I take that as a gross over-compliment to be honest. And also! When the hell has Steven Moffat seen me in my pants alone?”

Delia’s realisation of the Doctor Who theme is just one small example of her genius and we’ll demonstrate how the music was originally created as well as hearing individual tracks from Delia’s aborted 70’s version. We’ll also feature the make-up tapes for her celebrated piece ‘Blue Veils and Golden Sands’, and hear Delia being interviewed on a previously ‘lost’ BBC recording from the 1960s.

He is still the same man but I think my Doctor is a bit more reckless; he's a thrill-seeker and addicted to time travel. He is the mad buffoon genius who saves the world because he's got a great heart, spirit and soul but he also doesn't suffer fools. I hope all of these things come across but I think I've also injected a bit of my own personality into the role. I also helped choose the Doctor's costume which was great fun. Steven Moffat was very keen the outfit isn't seen as the overriding factor of the Doctor's personality but we still needed to find something that felt right. We tried on lots of things but kept reaching a dead end and we dismissed a number of items including a long leather coat, a long blue coat and some short punky stuff! But then one day I brought in my braces and a tweed jacket and it went from there. Soon we had the whole outfit although something still felt like it was missing and I asked if I could try on a bow tie – at that point the execs all bowed their heads in concern but luckily when I tried it on we agreed it worked and it has sort of become the signature of my Doctor now.

[The TARDIS is] like a Ferrari, Lamborghini and Porsche all moulded into one! It's so incredible because the TARDIS is an icon of our cultural history and suddenly I'm the one who's flying it. I am quite clumsy though so I kept breaking parts of the console and the poor production team had to keep fixing it. But the TARDIS is a magic concept and it provides a constant source of wonderment and adventure for both the Doctor and the viewers.

Well, for a start Steven Moffat has written a brilliant character. I do think Amy is different from previous Companions because she's very equal to the Doctor. She doesn't take his word as gospel and she's always happy to challenge him. If he tells her to do something then she won't necessarily do it, she might go off and do her own thing which can sometimes create a rift between the two of them! They are best pals though and it's a very up and down relationship because they are both very passionate people.

The Doctor is definitely an alpha male and Amy is an alpha female, so when they meet, they combust. They have quite a turbulent relationship but it's also really passionate and they care about each other. Amy can really hold her own against him and Steven's written some great one-liners. It's a great relationship.

I think it's quite important that I feel like her when I wear the clothes. So I worked quite closely with the costume designer, Ray, and also the producers, to come up with the signature Amy look. They were generally vintage clothes, but we tried to incorporate high street styles as well because Amy is young. I think naturally there is going to be some of me in her style, as I relate to Amy and we are the same age as each other.

I had a clear idea, which actually turned out to be the absolute opposite of what we ended up doing – which always happens when you get the casting right. I actually remember at the beginning of the process when I got a little bit cross whilst looking at the list of actors as it was full of people in their twenties. I said to everyone that we couldn't have a Doctor who is 27. My idea was that the person was going to be between 30–40 years old, young enough to run but old enough to look wise. Then, of course, Matt Smith comes through the door and he's odd, angular and strange looking. He doesn't come across as being youthful at all, in the most wonderful way.

The challenge with casting the Companion is that there are only so many people that would actually go through those blue doors. It has to be someone that loves adventure and doesn't quite feel at home with where they are. They have to be a feisty, fun-loving and gutsy person – and now we've got Karen Gillan. She was just exactly right for the role despite inhabiting Amy Pond in a way that was quite different from how I originally wrote the part.

It has definitely been a big challenge taking on this show because we love it so much, and why tinker with something that has been as popular, successful and brilliant as it has been? But at the same time we are terribly aware we have to look forward and work out how the show is going to survive in the future. In 2005 the team looked at what was fresh and new then and we have to do a bit of that ourselves. Looking at the episodes we've filmed so far we're starting to see the impact of those changes; what the team has managed to achieve is pretty thrilling.

The thing which is most important to us is telling a good story at the end of the day; that's always the thing the audience is going to be most demanding about. Beyond that, any changes we have made have been motivated by giving the show the best production values money can buy. It's the nation's favourite, and that means it deserves the best.

It is the biggest show on British TV in terms of the level of technical expertise everyone has to be versed in. There were new challenges for Beth and I as we had limited experience in dealing with prosthetics and complex CGI. However, I think the biggest challenge was to move everything forward and make the right calls on what to change and what not to.

Matt Smith: The idea is magic. Time travel and the TARDIS are just brilliant concepts and within the context of television it gives writers the opportunity to pen amazing stories because they have the scope to go anywhere and do anything. Doctor Who is infinite in its orbit and imagination and so it has fulfilled audiences' desires throughout the decades and will hopefully continue to do so in the future.

Steven Moffat: I think it is centrally vital for Doctor Who that at its heart and in its soul it is a children's programme. Not one that excludes adults, but one that welcomes them in. But when Doctor Who is really working, when it really delivers, the entire audience is eight years old – whatever age they started out!