It was the kind of crisp, bright January morning that made the residents of Richmond, Surrey, glad to be living out of London's congested West End.

The Thames glistened in the early morning sun," writes Lynda La Plante in the opening chapter of her international bestseller, The Red Dahlia. All seems well in this idyllic landscape, but within a paragraph a young woman's naked body - severed in two at the waist, her mouth slashed, giving her a clown's grimacing smile - has been discovered.

This is, of course, vintage La Plante territory and the story was filmed as part of her addictive TV series, Above Suspicion, starring Ciaran Hinds and Kelly Reilly as the ambitious DCI Anna Travis, La Plante's younger, post-feminist version of Prime Suspect's punchy, perfectionist Detective Superintendent Jane Tennison.

We meet on the kind of sunny, bright summer morning that must make the residents of Richmond, Surrey, of whom La Plante is one, glad to be living out of London's congested West End.

We're in a sumptuous hotel suite, with walls as purple as some writers' prose, although not, I hasten to add, that of the Bafta-laden La Plante.

Her baronial-style home, the palatial Petersham Hotel in Richmond, overlooks the spot where that fictional horribly mutilated corpse was found. It's enough to give you the shivers as you gaze at the willowy, green English landscape, with the Thames glistening in the early afternoon sun.

Such is La Plante's gift for grisly storytelling that she's adept at making the hairs on the back of the neck stand to attention. Indeed, she does so brilliantly in her latest ingenious offering, Wrongful Death, her 18th crime thriller, in which Travis reviews a cold case involving an apparent suicide. Inevitably, things hot up, with Travis taking in a stint with the FBI at the Quantico training centre in the US. Needless to say, La Plante has been there. "Only fleetingly, but I met the guys and I've researched every last detail because I always want to get it right."

Get it right she does but there seems to be no end to the scope of her powerful imagination, as her legions of fans know from her bestselling thrillers and the many major TV series she's created, from the groundbreaking Widows to Prime Suspect and Trial And Retribution.

Famous for her scrupulous research into the evil that men, and some women, do, is there nothing she couldn't turn into crime fiction, any true story so harrowing she couldn't make it up?

"Yes, there is," she responds as we share sofa space in a swish sitting room opposite a blank TV screen, which if it were showing a La Plante programme would have me on the edge of said sofa. "I could never have made up the Jimmy Savile sex abuse scandal, or indeed the spate of high-profile celebrity arrests that followed," she sighs.

Now an ebullient 70, with a mane of maple-leaf red hair, La Plante was a successful actor - Lynda Marchal - in the 1970s and early 1980s, appearing on stage opposite Anthony Hopkins and with the Royal Shakespeare Company and the National Theatre. She was a regular in TV series such as Z Cars, The Sweeney and The Professionals ("Always playing prostitutes, though," she giggles).

Did she ever meet Savile?

"No, I didn't. But I always thought that he was repellent. Horrible man. Those rings on his fingers, that awful hair … It beggars belief that he was given the keys to a mortuary. Was he a necrophiliac? It's just horrendous," she replies in her plummy RADA-trained accent.

"I feel so strongly about this shocking business. To me, it's pointless putting an 83-year-old man like Stuart Hall in prison for a few months for what he did [we spoke before Hall's jail term was doubled]. Ditto all of them when it comes to imprisonment. You have to hit them where it hurts - and that's their money. Don't put them in prison. They have to be moved around, segregated in case of attack by other prisoners and given medical care lest they die of heart failure. Stuart Hall - what's his house, with its pool, worth? Millions.

"That's where you hit them. Take their millions from them. Nobody ever considers the victims, so that money should go into a pool for them. Hit every single internet site putting out any form of pornography. Fine them. Fine Google. Fine them millions. Tell them, 'If you go on putting out pornography, we'll fine you - £1.5 million for every 10 minutes, whatever.' They'd soon stop. It's not a witch-hunt of people like Hall as some people are claiming. It's one courageous person coming forward and having the guts to say, 'He did this to me,' then another comes forward and another and another … I just hope their victims can get some sort of compensation."

She pauses, takes a sip of water and says that it angers her even more that so many people were complicit in the abuse Savile subjected his victims to. "They knew these men were going after young girls, particularly Savile. Everybody knew he was dangerous around children, yet the BBC allowed him to have a caravan on their premises. So how many hundreds knew what he was doing? They claim he threatened to remove his charitable funding. What about his victims? So, no, I couldn't have made this story up.

"Look at [Ian] Brady and [Myra] Hindley. She got all possible help, from guitar lessons to degrees in psychology in prison. Who helped those grieving mothers who were never able to bury their children? Nobody. Consider little April Jones - look at that man [Mark Bridger, who was found guilty of her abduction and murder]. Look at Tia Sharp, the 12-year-old murdered by her grandmother's partner. Those girls' faces … The murder of a child imprints on everybody's soul. You never forget them. I've such hatred of these paedophiles - and it seems there are more of them around."

The award-winning grande dame of noir, who has created so much darkness in the name of entertainment, sees terrible darkness everywhere in today's world: a bleak landscape of crime and alienation, an apparently unstoppable flood of stories about sex crimes amid a tide of pornography on the internet.

She adopted an American-born baby, Lorcan, after years of fertility treatment and several miscarriages.

He's now 10 and La Plante, a single parent, fears that children's brains are being "saturated' with pornography. The other day she found her son sitting at the computer searching for a favourite band, Black Eyed Peas. "He said, 'This stuff keeps coming up, Mummy. I'm not looking at it.' It was shocking, disgusting stuff - filth. He didn't even understand it. Dear heavens, what are we doing to our children? It's horrible what's going on."

She believes part of the problem is that male judges and lawyers do not understand the terror of child abuse from a man or the psychological damage of rape. "The only ones that understand it have been abused as children themselves, or attacked in prison, say. The majority of adult men do not understand rape. There was a case where a man got off a rape charge because he 'didn't understand how to treat women'. What?" She thumps a cushion in bewilderment.

There will never be a La Plante storyline involving child abuse or murder, she insists. "There was one child murder in Trial And Retribution, but I'll never write another."

Did she write that before she adopted her son? "Yes, but having Lorcan hasn't changed how I feel about this, becoming a mother has nothing to do with it. The Trial And Retribution story was based on a true story. I spoke to the child's mother and to the policewoman, who had to tell her that her daughter was dead. She said the mother let out a howl, the like of which she'd never heard. The filming of that programme affected everybody - the crew, the actors. It was very, very distressing. I remember thinking, 'I don't want to subject myself to that any more. Never again will I create easy emotion out of the murder of a child.'"

Renowned for her forthright, opinionated views about today's commissioning editors in TV networks, the sparky La Plante consistently shoots from the lip. "What I find sad is that, with the success of Scandi-noir, which I love, everyone is now running around going, 'Oh, we want a 12-hour series.' For years they have been telling me to forget two-hour dramas because they can only afford an hour, always starring a famous actor, who is, of course, bound to be the villain, therefore destroying all credibility.

"The irony for me is that Sarah Lund of The Killing could never have happened without Jane Tennison and Prime Suspect."

Recently, she's been discussing an idea for a 10-hour series based on a true crime, in which a young police officer became obsessed with a beautiful, nameless murder victim. "Will it ever happen? I honestly don't know," she says, elegantly shrugging black, designer-clad shoulders. "My thing is twists and turns of plot, which is what I have done in my new thriller, Wrongful Death. I am not interested in getting into the mind of a psychopath. For me it's all about solving the puzzle; it's about craft."

She didn't watch BBC Two's The Fall, the recent ratings hit, starring Gillian Anderson and created by writer Allan Cubitt. "I couldn't watch it because I am not interested in the glorifying of a serial killer," she says.

A few days before I meet La Plante, a TV profile of Dame Helen Mirren was screened. "Not one mention of my name," La Plante fulminates.

"Then they say Prime Suspect made her career. I totally gave her career that kickstart. She was a classical stage actress, unknown on TV, and that's why I chose her to play Jane Tennison, which she did superbly."

Born Lynda J Titchmarsh and raised in Liverpool, La Plante had a happy home life as a child, the youngest of three. Her father was a salesman. There was no acting tradition in her family, although her cousin is former actor-turned-writer Fidelis Morgan, who worked at Glasgow's Citizens' Theatre. "As a child, I was cherished," says La Plante. At 15, she won a place at RADA and her Scouse accent was soon elocutioned into oblivion.

For 17 years she was married to American musician Richard La Plante. We'd been talking about bereavement so I ask if she grieved over the break-up of her marriage. She roars with laughter: "I was glad to see the back of him!"

She pitched her ideas for several TV series to the late producer Verity Lambert when she couldn't find any decent roles. "I thought I'd write one for myself. One came back with 'This is brilliant' scrawled across it by Verity. It was Widows [the 1983 series about a group of women successfully carrying out the bank raid that their husbands had died in the process of attempting].

"When I went in to see Verity, she said, 'Oh, it's you.' She looked disappointed, because she knew me only as Lynda Marchal. I'd just done The Gentle Touch with her. She said, 'We couldn't wait to meet Lynda La Plante, because we thought it must be a transvestite truck driver.'"

Her acting skills are a writing tool. "I talk to myself; I laugh: I sob uncontrollably when I'm sitting at my computer," she says.

"My acting ability is most useful, though, when I'm facing some absolutely disgusting piece of humanity in a prison and I need them to tell me stuff. Out comes the performer, 'Oh, I'm so pleased to meet you','' she says, oozing charm and doing another of the dozens of hysterically funny voices she has entertained me with over the past hour.

Finally, I ask La Plante whether she ever pinches herself in wonder at the extraordinary life and career she's had - in addition to the home in leafy Surrey she has a house in the wealthy Hamptons on New York's Long Island, where she and Lorcan spend summer.

"No, I don't," she responds. "I've worked so hard for everything and my life is still outrageous. Next year I've a stage play in the West End; it's my first. It's called Murder Weekend and it's a hoot, but very frightening."

The next Mousetrap?

"Ha ha ha! I wish …" she laughs. "I do stop and think, though, when I get an accolade such as becoming the first lay person awarded with an honorary fellowship by the Forensic Science Society or the CBE [she was appointed in 2008 for services to literature, drama and charity]. That was just amazing. It made me very proud of what I've achieved. That's when you get respect."

Respect, indeed, to the Dark Lady of Crime and her dark materials. n

Wrongful Death by Lynda La Plante is published by Simon & Schuster, priced £18.99. The author will be in conversation on Wednesday at 7pm at the Steps Theatre, Central Library, Wellgate Centre, Dundee. Tickets are free. Widows, The Governor, Above Suspicion and Civvies have just been released on DVD. Visit