LONDON (AFP) – Murder mystery writer Agatha Christie  was fed up with Hercule Poirot but kept on penning stories about the Belgian detective under pressure from her publishers, her grandson has revealed.

Christie considered the diminutive, stiff-moustached gastronome as her "bread and butter" but would grumble about having to churn out "yet another Poirot," Mathew Pritchard told Radio Times magazine.

"She was never short of ideas for books but some of these ideas were inappropriate for Poirot, so she was very keen to exorcise herself of him by writing different stories with new characters," he said.

"But her agents and publishers, who were in charge of the pounds and pence, were very keen on Poirot -- he was her most popular character."

Guinness World Records says British writer Christie is the best-selling author of all time, shifting more than two billion books.

Her most famous novels include "Murder on the Orient Express" (1934), "Death on the Nile" (1937) and "The Mirror Crack'd from Side to Side" (1962) and she also penned the play "The Mousetrap" (1952).

Poirot and Miss Marple were her best-known recurring characters.

Christie signed over the rights of her favourite works to her daughter and grandson before her death at the age of 85 in 1976.

"She was a very generous person and when I was nine she signed 'The Mousetrap' over to me," Pritchard said.

"I was too young to appreciate it at the time, but it now has a business history as long as my arm."

He was 10 when he first took one of her books from the shelf at her cliff-top home in Devon, southwest England.

"It wasn't one I would choose for a 10-year-old. There are 10 murders in 'And Then There Were None' and some are pretty gruesome," he said.