Agatha Christie would have approved of changing the protagonist’s heritage from white to Nigerian in the BBC’s TV adaptation of Murder Is Easy, her great-grandson has suggested.

This year’s BBC Christmas Christie adaptation has cast David Jonsson as the protagonist Luke Fitzwilliam, a young man forging a career in Whitehall until a mysterious encounter drives him to investigate a murder in an English village.

Asked by the Radio Times what Christie would have made of changing Fitzwilliam’s heritage to Nigerian, James Prichard, 53, said: “Rule one: I never try to second-guess my great-grandmother – therein lies madness. One of the things I hold to is that the first few adaptations of her plays were done by other people, and she didn’t like them because she didn’t think they were radical enough for the change in medium.

“She recognised that, when you shift the medium, you need to shift the story. It does give us a degree of licence to change things, but I also believe these are adaptations, not translations, and you are always looking at the story from where you are now, 90 years after this was first written.

“But the story remains central, as does something essentially Christie. I think we know what it is, and whether it’s there or not. And it’s definitely there in Murder Is Easy.”

Publishers have been using sensitivity readers on Christie novels to remove offensive language around gender and race in an attempt to preserve their relevance for modern readers. In March, new editions of several novels were published that had been edited to remove potentially offensive language, including insults and references to ethnicity.

Prichard said he felt that Christie’s work was in ascendancy again after being in the doldrums for much of his lifetime.

Citing the BBC’s decision to run an annual Christmas Christie since Sarah Phelps’s 2015 production of And Then There Were None and Kenneth Branagh’s Poirot films, including this year’s A Haunting in Venice, he said: “I probably shied away from it when I was younger – Agatha Christie wasn’t very cool.

“I don’t think in my lifetime she has been taken as seriously and enjoyed as much respect as now. Book sales are not just holding up but growing; stage performances, too. It’s just extraordinary how she stays popular and in demand.

“There are a lot of people who, in the past, might have read Agatha Christie as a guilty pleasure but are now upfront about it. Stars like Hugh Laurie, John Malkovich, Kenneth Branagh want to get involved. People take her seriously and realise her gift for storytelling was second to none.”

Prichard remembers his great-grandmother as “a pure and simple old woman” and has distant memories of spending time with her until she died in 1976, when he was six. “I came back from school and she was the lead item on the news. That’s when I realised she was something quite extraordinary.”