East London-born Idris Elba, who has also starred in Luther, has confirmed to a Hollywood entertainment website that he has been cast to play the former president and is expected to sign contracts this week.

He joins an illustrious group of actors who have imitated Mr Mandela in previous films, including Morgan Freeman, Terrence Howard, Sidney Poitier and Danny Glover.

However, none of those who have played Mr Mandela in major television and film productions are South African, and the omission has become something of a sore point with his countrymen.

According to Long Walk to Freedom’s casting agent, Moonyeenn Lee, none can measure up to Mr Mandela’s 6ft 4ins (1.93 metres) frame.

“I was free to cast a South African and I auditioned some extraordinary local actors,” Mrs Lee told South Africa’s City Press newspaper. “But the main problem is the height. Mandela is a particularly tall man. On average, South African actors are not 1.9m.”

She said that apartheid still casts a long shadow over home-grown acting talent, ensuring that few over the age of 40 have sufficient experience on major projects.

“The younger actors have had a chance to go and study and learn and work with internationals,” she said.

“The older actors, growing up during apartheid, had to deal with the cultural boycott, very few roles on television and almost none in film. There simply aren’t enough actors to choose from.”

Meanwhile Elba, she said, had immediately proved he had the star quality to play Mr Mandela. “When Idris walks into a room, there’s not one person who doesn’t look at him. He’s just got the aura,” she said.

It is not the first time that South African actors have been overlooked to star in films about crucial chapters in their own country’s history.

There was outrage when former Dreamgirls actress Jennifer Hudson was cast to play Winnie Madikizela-Mandela in Winnie, which is due for release this year.

Adaptations of South African crime writer Deon Meyer’s blockbuster books are also expected to star Hollywood actors in the lead roles.

Mabutho Kid Sithole, president of the Creative Workers Union of SA, who led the protests against Miss Hudson’s casting, said the height issue was simply an excuse.

“We are not impressed. So no one is tall enough? There’s always some reason to avoid using South African actors and having other people tell our stories,” he said.

“They use these stars for commercial reasons and the problem is South African business is not funding our own films.

“We see this happen over and over. Tomorrow there will be a film about Walter Sisulu and then what? No one is short enough?

“You tell me now, how will this actor pronounce Qunu where Mandela was born or Rolihlahla, his real name?”