David Walliams plays Jack Barker, the Prime Minister in The Queen And I...

Your character is pretty much the catalyst for everything that happens in the story. Can you tell us a bit about him?
Well, I play a very left-wing leader of a political party called the Republican Party, and one of my election promises is to get rid of the monarchy. Even unexpectedly to me, I become prime minister, and then feel like I have to go through with it, even though it feels like a mistake. He's quite fun to play because he starts off very bolshie and confident and by the end of the piece he's sort of rolled up in a ball on the floor and he can't believe what he has done.

Did you base your portrayal on any real world leaders?

Well, I'm not Daniel Day-Lewis, but I did look specifically at interviews and speeches from one or two politicians. And I looked at Jeremy Corbyn quite a lot. He's probably the closest we have to a radical left-wing leader.

You've met the real-life Queen. What was that like - did it prepare you for this in any way?

I've met the Queen at certain functions but I don't feel I get to know her because she's in Queen-mode. She must be very different with her friends and family, but she's very charming. She makes you feel very special, she understands that it's a big deal to talk to her. She just deals with it brilliantly, but it's difficult not to be totally in awe.

I've met other well-known people, but I've never had the same feeling as meeting the Queen. It's because she's in a role - it's almost like meeting a character. I think most people, whatever they think about the Royal Family, when they meet the Queen, they're immediately on their best behaviour. She's had a pretty incredible reign and she's played it so brilliantly that you've got to kind of hand it to her.

I've also done some charity events with Prince William and Prince Harry - and they're just really playing it brilliantly, because I think it's a pretty difficult role. Everyone wants to meet them, they can bring lots of attention to subjects that they care about and they have to work pretty tirelessly doing good. I can only liken it to when I've done book signings and you're meeting lots of people quite quickly, and it's great, but you can't talk to anyone for too long, because you've got 500 people waiting. They're doing that all day every day on an endless charm offensive and you never see it crack. I think it's a pretty weird thing to be born into, so it's how you deal with that.

How did acting opposite Samantha Bond as the Queen compare?

I love Samantha. I'm a huge James Bond fan, so I've taken part in a documentary about James Bond where I interviewed her [Samantha plays Moneypenny in the Bond franchise], and we got on well because she's super fun and she's got a real twinkle. She's a very funny lady. Occasionally we'd bump into each other and have a great chat, and then I was like: oh yeah, she'd be brilliant.

Because this is a sort of alternate reality as well, it's not a documentary, it's very much a version of these characters. We didn't want an impressionist, because it just wouldn't have sustained. You've got to really buy into her as a character. So, yeah, Samantha was fantastic and I really liked working with her because she's very easy going and she wants to help you as well. You're only as good as the person you're working opposite and she sort of makes you raise your game because she's so brilliant.

How do you think the public would react if the monarchy were abolished in real life?

It's kind of complex, but probably, people who think they want it may well regret it. There's something very reassuring about someone being the heart and soul of the nation and someone being beyond politics. I saw the brilliant play The Audience, about all the different prime ministers she'd had over the years, and you think, there's something really reassuring about someone being there the whole time. So, I think you would miss it.

Do you think the story says anything about class in Britain?

Yeah. Lots of other countries scratch their heads at our class system and obviously it does come down from royalty. I find class bizarre. Some people are born into poverty and some people are born into riches and you can't make sense of it. It's just the way the world is. And people move through the classes - if you're the son or daughter of, say, a very rich, famous rock star who was working class, you sort of become upper class really, and it's kind of weird. I mean my parents were working class, but they saw that they wanted to be middle class. It's not that they weren't proud of being working class, but those were the aspirations they had at that time.

If you were prime minister for a day what law would you pass?

I always think politicians are the lowest rung of showbusiness. There they are, on TV, talking and doing rallies and that, but they always seem so utterly miserable. Even when you're prime minister, I think it must be fun for, like, a day, but then the criticism comes in.

Also, I think people hate politicians just for being politicians. I think it's a really difficult job, so I wouldn't want it. But I think most people who are left wing would like a fairer society. I'd happily pay more taxes so that we've got better schools and hospitals. That's what I'd do, raise taxes for people like me and spend some more money on those services for people who need them.

Do you think there are any gaffes or scandals you'd fall victim to if you were PM? Theresa May's dancing incident, for example...

All of them! I think if the worst thing Theresa May has done was dance... come on. She knew what she was doing. She was trying to give a human side of herself that people don't perceive is there very much because she's quite a straight sort of person. She just reminds me of a sort of head girl, who doesn't really know how to have fun. But that's OK, she's not really meant to do that is she, she's prime minister.

Seeing as The Queen And I is going out at Christmas, what's on your Christmas list this year?

I generally just like books. Beautiful books of photos... biographies...The kind of things that people probably wouldn't think I'd be interested in, like Max Hastings books, a book on the Vietnam War, the biography of Eric Clapton... Eric Idle's autobiography - I really want to read that - because I love the Pythons and I've met him a few times, so I find him fascinating.

I like reading about showbusiness from the past because it always seemed more glamorous. I guess celebrity has become slightly devalued by having reality shows and all that sort of thing, whereas then you were super famous if you'd achieved something. There wasn't social media, so you were a little bit more on a pedestal.

And what do you think Christmas Day at the prime minister's house is like?

Do they have it at Chequers? I once went to Chequers when David Cameron was prime minister and he showed me the library - just me and him - and there were all these beautiful leather-bound books. Like, there was book of British martyrs or something, just fascinating stuff that I'd never seen before in my life. So it's an incredible thing for the time you're prime minister having access to all these things. But what would Christmas be like? Probably a little austere, because if you're prime minister you can't be seen to be spending any money on yourself. I bet they get everything from Aldi.

Do you have any Christmas rituals of your own?

The thing I really like is being able to eat sausage rolls at about five in the afternoon. There's some weird thing about food, isn't there - all food rules go out of the window. It's like midnight and you're eating your own body weight in stilton and you don't really know why. But there's something brilliant about that, it's a sort of indulgence isn't it. And I know maybe I'm privileged I get to do these things, but to me it's about having some hot sausage rolls with brown sauce and watching a Bond film. I couldn't be happier than that.