David Suchet plays Dr Fagan, the head teacher of the inadequate Llanabba Castle where Paul Pennyfather finds himself teaching.

What drew you particularly to this production?

Two things really: Evelyn Waugh, who I think was one of the most extraordinary writers, and his book. Decline And Fall was so well-known and I read it many, many years ago.

Was there anything you brought to this role that was different to your previous work?

Well, I'm obviously known more for straight roles, even though Poirot himself has a sort of comedic aura around him in certain situations.

The last time I really did a comedy was Blott On The Landscape and that goes back a very long way. But Tom Sharpe, who wrote Blott On The Landscape, also wrote Porterhouse Blue, and if you look at that, or read that book, it's very similar in style to Evelyn Waugh, so I've almost come full circle!

Do you think you needed to update how your character behaved in any way?

Not really. Adapting a novel for the screen is something that I've been doing most of my filmic career. If you think, I've done over 70 Agatha Christie films that are based on her books so all of those are adaptations. It is, I think, a wonderful and faithful adaptation of Evelyn Waugh's book.

You tackle some difficult territory when thinking about some of the things that come out of Fagan's mouth. What do you think motivates Fagan and how did you bring his character to life?

I think one has to remember the style of the book: it's realistic, but not totally naturalistic. Therefore, the characters are heightened and satirised.

My character, being the head of this crazy school with crazy boys, the headmaster is a crazy guy! He's eccentric, he's pompous, he's more interested in money, show, exteriors than he is about anything else, so that's what drives him and that's all he really cares about. So his morality is really as a result of his world view.

Some of the territory is frankly not politically correct at all, especially to modern ideas, is there protection offered by this sort of bubble of a world?

Because it contains much which is amoral, the book in its day would have been absolutely shocking! I don't know how shocking it will appear today. This is going to be interesting because there will be a young audience coming to this because of Jack, and I will bring a certain older audience. So we will have two sets of PC values going on. It will be fascinating to see what the results are.

I can only play the truth of my character within a given situation and that's my responsibility. As far as my character is concerned in this piece, I think it's joyous.

What do you think Waugh would have made of this adaptation?

Well, wherever he is now, I hope he will see it, that he will watch it, that he won't necessarily do catch-up and see it as it goes out! My hope is that when he sees it he will be very happy, he will laugh, he will smile, and be very proud that he wrote a book that is faithful and - hopefully - successful on film.