David Walliams has guest starred in many shows. Here he talks about his involvement in Blandings...

Talk us through your character, Rupert Baxter, please David...

Connie brings Rupert in as a secretary to organise Clarence's life. Rupert is very fastidious. He is quite contemptuous of the upper classes. He's middle-class and wants to organise everything, but Clarence ends up as his nemesis.

What attracted you to Blandings?

I adore PG Wodehouse. I have loved him since first reading Jeeves & Wooster when Fry & Laurie played them on the TV. Even then, I realised that Wodehouse is a comic master. As soon as I got the call about this, I was desperate to do it.

Any other reasons?

Yes, unlike some things I've done, this is not rude. It's family orientated. It's come at the right time. There is currently a big renaissance in costume dramas, but there hasn't yet been a comic one.

Does Blandings also represent quite a change of tack for you?

Absolutely. When I did Britain's Got Talent, I was quite concerned that once you've appeared as yourself in such a major way, it might be hard to go back to acting. Actors should have some mystery about them, and it's hard to accept them in roles when you know too much about them. So it was great to be offered this part. Also, I've not done that much period in the past.

Were you eager to work with Timothy Spall, too?

Yes. I know Tim quite well because I've worked with his son Rafe before. I'd always thought that I would love to work with Tim as he is one my favourite actors, and the experience was not disappointing. What is excellent is that he's not obvious casting as the aristocratic Clarence. You see him in Mike Leigh films or Auf Wiedersehen, Pet and he's very different. He's such a great actor because he can do anything. A lot of actors have played silly posh characters in the past, but Tim can do it in a very original and very funny way.

Why do we like period drama so much?

I used to watch Jeremy Brett's Sherlock Holmes at home and my mother would say, "Where did they get that china from?" She was not at all interested in the mystery. Much of the interest in costume drama stems from the production values. Yesterday I was driving a Royal Enfield vintage motorbike on set - where else would I get the chance to do that? I love all the clothes, the shoes, the jackets the collars and the tie pins. I'm obsessed with details.

Are these stories still relevant?

Yes. They may seem at first to be quite frivolous tales about, say, a misplaced letter. But there is actually quite a bit of social satire in there which will chime with audiences. Class still dictates a lot of things in this country. But above all, these stories are very funny and that's why they have endured. Good humour lasts.