David Walliams talks about the origins of Gangsta Granny in this interview. You can watch the video, or read the words:

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On the origins of Gangsta Granny...

Gangsta Granny started off as a book which, incidentally, is written by myself. It's the story of a little boy called Ben, who thinks his granny is very, very boring and hates spending time with her... until she tells him that she was an international jewel thief, and they go on an adventure together to steal the crown jewels. There is a mystery however as to whether she really was an international jewel thief or not.

It's about old people, and the way young people think about old people, because I think young people think old people were always old and nothing exciting ever happened to them - and certainly I used to think that when I was 8, 9, or 10 with my grandma. Then I'd get them on a subject like the Second World War and talking about living in London through the Blitz, and suddenly they'd come alive, and that's literally what I was thinking about when I wrote the original story.

On his character, Mike...

In the book of Gangsta Granny, the parents are in the background a bit but in the script they've come to the fore a little more. So I'm Mike, Miranda Hart is my wife Linda, and we're both obsessed with Strictly Come Dancing to the extent where we want our son, Ben, who is obsessed with plumbing, to become a ballroom dancer. You see us, in the film, ballroom dancing with each other which is a lot of fun.

Suddenly we got the bug for it and we were thinking "ooh, we should be on Strictly!"... Miranda was marginally better at it than me, but neither of us were very good. We run a spray tanning salon called 'Browned Off' which is why we've both got these terrible spray tans.

At the start of the story we're quite neglectful parents, we're quite selfish - we just tend to dump our son at granny's house every Friday night so we can go off and enjoy ourselves, and if Ben speaks when Strictly is on he gets into trouble. So we're not the best parents in the world, but things come good by the end of the story.

On adapting Gangsta Granny for television...

I've had a fair bit of input in turning Gangsta Granny from a book into this TV version. The script was originally written by Kevin Cecil and Andy Riley, two brilliant comedy writers who wrote Gnomeo & Juliet, amongst other things. They adapted the book first, which was great, because it was fresh sets of eyes on what I had already done. Then I came in at a later date and we worked together on it.

I think with an adaptation - the book exists, it will always exist - and this is a chance to really build on the book - try and make it funnier, try and make it more moving, add in elements which weren't even originally in the book. I think sometimes authors can be too proscriptive about wanting to change any line, but I think it's a different medium, and because I come from writing for TV I understand that. You do hear horror stories about writers who've written famous book and they hate the idea that a word has been changed, but you just have to because it's something different. The other thing is that the book is almost exclusively aimed at kids, whereas the film is hopefully going to be watched by families, people of all ages, so you've got to make it work for a broader audience.

In the book, it's all pretty much from Ben's point of view, whereas TV doesn't work in the same way, you don't need to do that. You can cut from different characters and different points of view much easier. There are some scenes of me and Miranda ballroom dancing together, which aren't in the book, but they're a lot of fun. We even do a tribute to Torvill & Dean's Bolero routine which was fun - we drag one-another along the floor. I really enjoyed those.

I also just really love this cast we've put together. You think about your dream cast, all the people you can have - Rob Brydon as the nosey neighbour, Joanna Lumley as the Queen, Julia McKenzie as the granny - it's been great getting all these amazing people involved. Seeing what they do with it too. I like that the characters which I wrote on the page have really grown into these great comic performances.

On what he wants viewers to take away from the film...

What I hope young viewers will take away is the good lesson about old people not being boring just because they're old and they've got great stories to tell and information to impart to you. You've got to really relish that time with them, because when you're a kid, your grandparents are not going to be around forever and to hear all of their stories, it's really important otherwise they'll be lost forever. An adult watching it may be watching it through the eyes of Mike, my character, and Linda, Miranda's character, really thinking more about their children and listening to their children about what they want to do because Ben in the story wants to be a plumber but his parents are trying to force him into ballroom dancing. And then if there are grannies and granddads watching, they might have another view of it because they'll probably relate to the character of granny more, and the pleasure of telling amazing stories to their grandchildren, I suppose.

I just hope people are entertained, and moved, and that's it's just a great Christmas story. It's interesting because you get more perspectives than you do with the book. Although I do get a lot of grannies saying they've bought it for their grandchild and they like reading it. When I do book signings I get a lot of grannies saying to me "I'm a Gangsta Granny!" so it seems to have caught on the idea, a little bit.

On how Gangsta Granny ties in with the festive season...

I think Christmas is the time when families get together if they can, and it's a time when you think about the people who aren't there, people that you've lost. There is a sad element to the story... I hope it captures the sometimes bittersweet feeling you sometimes have at Christmas, that you're all enjoying yourselves but there are people that you're missing. That has certainly been my experiences of Christmas in the past, so hopefully it's heart-warming but also acknowledges the sadness a lot of people feel if there's someone that they've lost in their family.