LYNDA LA PLANTE arrives at the swanky Savoy Hotel in a white lace shirt and slacks, big red hair cascading over her tiny shoulders, as a waiter shows us to a table and she orders her regular BLT. She's understandably excited about her latest book, Tennison, the much anticipated prequel to the hit TV series Prime Suspect, which threw Dame Helen Mirren 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.
PRIME SUSPECT: Helen Mirren
You can taste the nostalgia, the flared trousers and roll-neck sweaters, the sexism of the 1970s Metropolitan Police force and the prejudice against women by male officers, who see policing as a man's job. Anyone who lived through that age and remembers the TV cop show The Sweeney and the unorthodox, often violent, methods of investigation, will recognise the era.
At her first post mortem, Tennison naively rubs Vicks under her nose to take away the smell of death, not knowing the ointment actually clears the nasal passages, so exaggerating the smell - just another ruse from an erstwhile male colleague.
The scenes involving examinations of the dead are graphic, the details of which bear witness to La Plante's painstaking research, having herself graced the tiled floors of mortuaries and witnessed numerous post mortem exams over the years. She is now an honorary fellow with the Forensic Science Society. "What people don't realise is how long an autopsy takes," she reflects. "In those days, it would take hours and hours. There was no DNA and even blood testing was spasmodic."
A natural raconteuse, anecdotes drip off her tongue easily in an impressive range of accents, a legacy of her acting days, before the Rada-trained Liverpudlian with the plummy voice gave up life in front of the camera to write some of the best dramas on TV, including Widows, Trial & Retribution, The Governor and The Commander.
Ever one to control the show, La Plante, 72, is involved in the casting for the forthcoming series and reveals she's been trawling drama schools up and down the country to find unknowns to play the key roles.
"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."
"I find the constant repetition of the same actors becomes almost farcical," she continues. "If you're in the middle of watching a drama, you'll think, 'Hang on, weren't they in EastEnders?' and you've missed a whole section because you're trying to place the actor.
"Look at the killer in Prime Suspect - John Bowe - nobody had seen him before and nobody had seen Helen Mirren on telly 25 years ago. TV people only knew TV people because they didn't go to the theatre."
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.
Tennison by Lynda La Plante, published by Simon and Schuster
"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."
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.
"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."
While the original Prime Suspect became an iconic series, La Plante withdrew her involvement after the third instalment, because she was unhappy with the way it was going. She didn't like a plotline which suggested Tennison had put away the wrong man, and was even less keen on the idea that she would end up an alcoholic.
"I have never seen the latter series of Prime Suspect. I had created what I thought became an iconic character. I would not have let her be a drunk. I thought she'd fought too hard. I didn't want to see the final series."
She places the young Tennison at Hackney station, a tough, rough patch, which seems fitting as her main researcher, a detective pal, had met his wife at Hackney when both were young uniformed officers.
"So I had carte blanche - whatever I wanted to know, they could tell me. Even funny anecdotes about eating their fish and chips underneath their capes - they had it all. I couldn't have done it without them."
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 says candidly. "If you come away from the book and you haven't cried, then I've failed."
Today, La Plante lives with her adopted son Lorcan, 12, in Kingston, Surrey, although she also spends a lot of time in New York, where her male companion lives.
She has had the same man in her life for some years, but tries to keep him out of the spotlight. He's a banker who lives in the US, but they catch up in the school holidays and she has no desire to get married again.
"Of course I worry about being an older mum. But there are people much worse off than me. As long as I can move my arms and legs and get about, it's OK."
In the meantime, there is no thought of retirement. Her production company is as busy as ever and she's planning at least four more Tennison books, because the character is still only 23 at the end of the first one. More TV adaptations may follow, depending on how the first one is received.
"It would stop abruptly if there was no incredible feedback," La Plante reflects.
"If everything stopped, the book didn't sell and no-one wanted it, then I'd say, 'Fine, it's time to retire'. But until that time, I love what I do and I'm surrounded by lovely people."
Tennison by Lynda La Plante (Simon & Schuster) £20
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