Lynda La Plante has admitted it will be a tough job to find the right actress to fill Dame Helen Mirren’s shoes for the TV prequel of Prime Suspect.

The respected writer has just published her latest book Tennison – the much anticipated prequel to the hit TV series, which threw Dame Helen into the TV spotlight almost 25 years ago, winning a clutch of awards here and accolades worldwide.

Her new novel rewinds to the Seventies, as the eponymous 22-year-old newbie WPC is drawn into her first murder case, the killing of a young girl who has been savagely beaten.

Lynda La Plante
Lynda La Plante (Carmen Valino/PA)

La Plante, 72, – who is responsible for a clutch of hit dramas including Widows, Trial & Retribution, The Governor and The Commander – is involved in the casting for the TV version of Tennison and revealed she’s been trawling drama schools up and down the country to find unknowns to play the key roles.

She said: “To actually find the weight of a Helen Mirren is going to be hard. I’m compiling a stack of photographs of possibles, but I’m not narrowing myself down to saying she’s got to have short blonde hair.”

It’s the first time the novel has come before the TV series – La Plante wrote the original Prime Suspect for television before it became a book. She’s now completed the six-part TV adaptation, which is due to be shown on ITV next year.

She had the idea of turning the clock back when she was giving a talk at a book event in Sheffield and a blind woman in the audience asked her what made Jane Tennison such an ambitious, cold, ruthless woman.

“I’d no background of her. I thought, ‘Where did she come from and, more importantly, how did she get to be that person who dealt with discrimination, put-downs and had the bottle to say, ‘I’m treading on dead men’s shoes’.”

La Plante has dedicated the book to Dame Helen Mirren.

“She was the consummate actress who took the role and dared to portray a woman without a hint of simpering female. Even today, when I’m talking through the script, co-producers will say, ‘Could we come out with a soft smile?’ and I’ll say, ‘No, she’s not smiling. Why would she be smiling?’ You can’t write a tough woman and let her be likeable.”

Helen Mirren
Dame Helen Mirren won awards for her role as Jane Tennison (Mark J Terrill/AP)

They keep in touch although they are not close friends, she admits. There’s more a mutual respect for each other.

“Whenever we’re at the same function we are delighted to see each other,” Lynda said.

“At some point, I would love to get her approval and to say, ‘Do you want to see yourself when you were young?’ But the reality is Helen Mirren has swayed the most amazing career as a big movie actress and she looks incredible.”

She hopes that the book won’t create a spoiler for the TV series, as people who’ve read it will already know what happens. “If you’ve read it, you’re going to ache to see it,” she said candidly. “If you come away from the book and you haven’t cried, then I’ve failed.”

Tennison by Lynda La Plante is published by Simon & Schuster, priced £20.