The classics have to be sexed up for TV, says the Witness For The Prosecution writer

People often ask me how I go about adapting a classic novel or short story for the small screen – and the answer is that you’ve got to be brutal. I’ve dramatised a number of classics for television, including Charles Dickens’ 500-odd page Great Expectations, Agatha Christie’s 250page And Then There Were None, and most recently her short story The Witness For The Prosecution, which aired on BBC1 at Christmas.

After finishing an adaptation I get nervous and keep thinking I could have written certain scenes better – so I was blown away by the success of my two Christie screenplays. And Then There Were None got almost ten million viewers, and The Witness For The Prosecution seven million.

Having said that, dramatising big fat novels and even short stories is always going to be a challenge. My main aim is to get to the heart of the story. But once I’ve got under the skin of the characters, the story just explodes in my head.

However, you’re inevitably going to end up losing characters and parts of the narrative. How to decide who stays or goes, or who warrants a bigger role? Some characters just come to the forefront while I’m writing, and others recede or have to be lost. It’s all about serving the central story.

So for instance, when adapting Great Expectations I was sad to lose the Aged Parent, one of Dickens’ finest comic creations. Other times, a minor character – such as Janet the maid in Witness – can become a main protagonist. You have to be tough, or else you could end up with 27 hours of TV that won’t necessarily be good.

You’ve also got to be brave. Some viewers might not be comfortable with changes I’ve made – the sexual content, swearing and violence – but these stories are violent. They’re about sex, money, jealousy, betrayal, extreme emotions and extreme behaviour. Christie wrote murder stories and murder isn’t polite. I don’t put these elements in to be gratuitous but to tell the story.

Another thing: if you’re going to adapt a literary classic, you have to immerse yourself in it 100 per cent. Sometimes I write for three days and nights, grabbing the odd hour’s kip. The outside world falls away and nothing exists but the characters – such as John Mayhew and Emily French from Witness, who were played by Toby Jones and Kim Cattrall. It’s a strange way to live.

I’d like to think Charles Dickens and Agatha Christie would approve of my adaptations, despite the changes I’ve made. But if they didn’t, I’d be prepared to argue the toss. It’d certainly make for an interesting dinner…

The Witness For The Prosecution DVD and Two By Christie DVD box set are available now.