The makers and stars of A Very English Scandal discuss why comedy is so important to the story

Scott (played by Whishaw) miraculously survived because the hired hitman had a phobia of dogs, and decided to kill Scott's Great Dane first. When he finally turned the gun on Scott, it jammed. Thorpe (Hugh Grant) was sensationally acquitted for conspiracy to murder, while Scott was laughed out of the court and ridiculed by the British public.

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Grant, who would have been 18 at the time, remembers the trial. “I do, I do,” he says. “I remember all the jokes. We were always just sniggering, really. I think the whole of Britain was sniggering.

“Let's not forget that Norman Scott didn't get killed in the end. Had he got killed it might have had a different tone to it. People felt very sorry for Rinka the dog. But, you know, the world was very different then, Britain was very different.

“Even gay sex was a source of much greater sniggering than it would be now. All the biting the pillow stuff was just hilarious and the courtroom erupted into laughter when that sort of remark was made.”

The series does have an absurdity to it: Grant takes on the persona of a pantomime villain and both the score and the performances are very buoyant. Grant’s scenes with Alex Jennings – who plays right-hand man Peter Bessell – are riddled with sly humour.

And the story itself is stranger than fiction. It has so many comic elements, for example: Scott had a Jack Russell called Mrs Tish, the hitman was an airline pilot who only agreed to kill Scott after 16 pints, and one of Thorpe's aides quit politics to become a manager of a roller-disco in Camden.

Russell T Davies, who wrote the screenplay, said his approach to the series was to try to encapsulate the nation’s mood at the time the story broke: “Even on the news, it was bizarre. It wasn't the lead item on the news… because only a dog was killed.

“I was 16 [at the time] and it was hard to understand the import behind that, the politics of it, the sexuality of it: that one dead dog was actually huge," he says. "But at the time it felt like, 'A dog? A dog was killed?'”

Davies said it was upon his realisation that the dead dog was a Great Dane that his interest in bringing the story to the small screen was really piqued. “I thought, 'That's going to look like I made that up. Like I just made the dog bigger to tell a madder story.' But it really, really was a Great Dane… it's properly mad.”

Keen not to take the whole thing too seriously, Davies sums up the Jeremy Thorpe affair as “a middle-aged gay man falling in love with a beautiful gay man who takes too much drink and drugs" before adding, "That's a Friday.”

Whishaw did acknowledge the sombre side of the story, in that two men were ultimately destroyed by a toxic love affair: “It’s also really tragic at moments,” he says. “And it's also savage what these people do to each other and what the establishment does to protect itself.”

However, it was the comedic aspect that ultimately drew Whishaw into the project: “I was really attracted to the humour of it, I found it very funny.”

Speaking of Davies’ signature ability to mix the dark and the light, he explains: “It's brilliant when a piece of writing captures that quality because it seems to me that's how life often feels. Even in the middle of something awful, you'll be laughing. That's a British thing.”

Director Stephen Frears says that he and Richard Ingrams – the former editor of Private Eye – agreed that Preston’s book was the “right” one to adapt given that it embraced the black comedy of the whole scandal. “[The story] was very, very entertaining. The whole thing was endlessly entertaining. That's what Richard Ingrams thought… That's the one that gets the tone right,” Frears says.

“It was so ridiculous the whole thing, just ridiculous… the incompetence just takes your breath away.”

A Very English Scandal begins on Sunday 20th May at 9pm on BBC1