Crime writer Val McDermid on her latest book Insidious Intent and the secrets to getting away with murder

McDermid, 62, is often asked whether advances in forensic science have undone the job of the crime writer. The thriller, which sees DCI Carol Jordan and psychological profiler Tony Hill return for their 10th outing, cleverly turns that notion on its head.

"I thought it would be interesting to have a killer who is very forensically aware and the usual routes of investigation run into the buffers," she says. "Everyone thinks that forensics solve everything these days, but there are still so many cases where for one reason or another you can't rely on the forensic science to give you the answers."

McDermid struck upon the idea of weddings as the murderer's chosen hunting ground after an illuminating conversation with a recently married friend. "She mentioned that three couples they knew had split up within weeks of the wedding. Apparently it is quite common for weddings to precipitate people getting together or splitting up.

"I started thinking about it and realised that, if you are looking to acquire a victim, someone on their own at a wedding is probably more open to the idea of romance than pretty much any other setting. There is a feeling of safety because everyone in that room has been invited by either the bride or groom. The sense of stranger danger is gone."

McDermid has a reputation for meticulous attention to forensic detail and as part of her research she spoke to world-leading experts Dame Sue Black and Professor Niamh Nic Daeid at Dundee University's Centre for Anatomy and Human Identification.

Black taught her how to break a hyoid, a small horseshoe-shaped bone in the neck. "We were in her lab and she was showing me the flexibility of the hyoid bone," explains McDermid. "She then handed it to me and said: 'You have a shot …'"

No sooner had the author taken hold of the bone than it promptly snapped. McDermid chuckles while giving a self-chastising head shake. "Clumsy lummox," she says.

Nic Daeid, meanwhile, shared her wealth of knowledge on fires within confined spaces, a topic McDermid found fascinating.

"Niamh showed me this amazing video of a Christmas tree fire," she says. "There is a living room with a synthetic Christmas tree in the corner and an electrical spark sets it on fire. Within 45 seconds, it is a room on fire. I watched this video with my jaw hanging open."

The discovery of charred human remains in the driver's seat of a burning car is among the grisly scenes that feature in Insidious Intent. McDermid's searing prose likens it to a Sunday joint roasting in the oven. "A nice leg of pork with plenty of skin for crackling," she writes.

It is this lyricism and verve, alongside her storytelling, which has won McDermid fans around the globe. She has sold more than 15 million books and been translated into 30 languages.

This year marks the 30th anniversary of the publication of her debut novel Report for Murder. McDermid has written close to 40 books including children's titles, non-fiction and short story collections (even she has lost exact count).

A shadow crosses her face when asked about plans to celebrate. "It is a weird thing for me because my dad died 10 days before my first book was published, so when the anniversary rolls round, that is always at the back of my mind. There is a bittersweet element to it where I never feel like celebrating hugely. But we will mark it, probably by going out for a family dinner."

A lifelong Raith Rovers fan, McDermid draws some solace from having been able to show the cover art to her late father Jim, who was a football scout for the Kirkcaldy club, before he died. "But he never got to hold the book in his hands and I'm really sad about that."

Although she can imagine what his reaction might have been. "Being from Fife, he would just have taken the piss," she smiles. "He would have been like: 'Aye, no bad …'"

Her working-class roots are an eternal grounding should McDermid ever become too big for her boots. "I remember a family funeral some years ago where one of my aunties came up and said to me: 'I read one of your books, didnae think much tae it.'

"In Kirkcaldy, it doesn't matter how many books I sell or what awards I win, I will always be Jim McDermid's lassie because my dad discovered Jim Baxter, who was probably the greatest footballer Scotland has ever produced."

The larger-than-life characters she conjures – fearless journalist Lindsay Gordon, shrewd private investigator Kate Brannigan and tenacious police detective Karen Pirie – leap off the page.

In 1995, McDermid began chronicling the adventures of Tony Hill and Carol Jordan. Her inaugural offering, The Mermaids Singing, won a Crime Writers' Association Gold Dagger and was adapted into an ITV drama, Wire in the Blood, starring Robson Green and Hermione Norris.

Insidious Intent – the latest Hill and Jordan instalment – contains a heartfelt letter from McDermid appealing to readers not to reveal spoilers regarding its helter-skelter climax.

"I've never done that before," she says. "But I have readers out there who have devotedly followed Tony and Carol for the last 22 years. They have a lot bound up in those characters. I don't want anybody to hear about it second-hand before they've had a chance to read it themselves."

McDermid is realistic that not everyone will respect her wishes. "There will be trolls who think the most fun thing they can do is to put it out there. So what? If that is how they get their kicks then you have to feel sorry for them to have such a limited and tragic world view."

In recent weeks, she has had fans asking if Insidious Intent will be the final outing for the intrepid duo. McDermid is keeping tight-lipped. "What I will say is that I've kept the promise to my readers that I will never kill Tony or Carol," she says. "They can be rest assured on that point."

She is lined up for a slew of appearances at the Edinburgh International Book Festival including as part of the Fun Lovin' Crime Writers, an ensemble comprising McDermid alongside authors Mark Billingham, Doug Johnstone, Stuart Neville, Luca Veste and guest vocalist Christopher Brookmyre.

"There is a bunch of us who are living our fantasy of rock stardom this year," she grins. "I'm the singer. My fingers aren't fast enough to play guitar in public any more."

Billingham, whom she describes as "the dreamer" of the band, has made Fun Lovin' Crime Writers badges and postcards. "We are living the dream," says McDermid.

They will perform as part of the festival's late-night Unbound strand and McDermid promises a very special appearance. "For one night only, [Icelandic author] Yrsa Sigurdardottir is going to do backing vocals on Sympathy for the Devil. A star-studded line-up."

The Fun Lovin' Crime Writers will also hit the stage at the Bloody Scotland festival in Stirling next month. "And we're available for bookings at weddings, funerals …" intones their charismatic frontwoman.

McDermid bats away the suggestion of any potential stage fright. "We are all used to being in public and have faced the prospect of making a complete arse of ourselves many times before," she says. "There is nothing new there."

She cites her earliest aspirations as wanting to be a writer or musician ("specifically Joni Mitchell, but unfortunately the job was taken") and to that end there is something poetic in McDermid living out that dual dream.

The milestone of 30 years since her first book gets us reminiscing. Not least about her "accidental" path into crime fiction. McDermid recounts childhood weekends and holidays spent with her grandparents, when she would turn up with a pile of library books under her arm.

"The only book they had in the house apart from the Bible was a copy of Agatha Christie's Murder at the Vicarage," she says. "I don't know why, I don't think either of them had ever read it. Whenever I ran out of books that was what I read. I must have read it dozens of times over the years."

Fellow crime writer Ian Rankin is also celebrating his 30th anniversary. They both hail from Fife ... "Something in the water?" she smiles. "We were lucky that when we were growing up Fife had such a terrific education system.

"It was top of its game and I think we both benefited when the quality of Scottish education was among the best in the world. Frankly, that is where we need to be again. If we are going to have the next generation of Val McDermids and Ian Rankins, we need to make sure kids have a good start."

In her final year at primary school, McDermid was chosen for a hothousing experiment. On the basis of an IQ test, she was placed with a group of exceptionally bright children at Kirkcaldy High School who were taught in a separate class, focused on preparing for university.

McDermid is bullish when asked whether a similar scheme could work in the modern era. "I don't think so," she says. "I think you improve it for everybody."

She famously became the first pupil from a Scottish state school to graduate from St Hilda's College, Oxford. McDermid believes that would be a pipe dream if she were a teenager today. "If I was 16 or 17 now I wouldn't be going to Oxford because I couldn't afford it," she asserts.

"I was one of that very lucky generation where I got a full grant and my fees were paid. I left university with £200 debt on my credit card. Kids nowadays have £40,000 or £50,000 worth of debt. That is a shocking thing to have round your neck."

At Oxford, where she studied English, McDermid buckled down for a journey of self-discovery. "There was a possibility to set your own account of yourself and I found that quite liberating," she recalls. "I had always felt like an outsider and different."

Reading Kate Millett's seminal feminist text Sexual Politics was key to her awakening. McDermid describes it as a "great lightbulb" going on inside her head. "I started hanging out with feminists and then I discovered lesbians, so that was very exciting. That made sense of everything."

Earlier this month, McDermid presented From Shame to Pride on BBC Radio 4, a series charting the history of same-sex relationships in Britain. On a personal level it provided an opportunity to pause and take stock of how far things have come over past four decades.

The author left Scotland in 1979 because she felt unable to live her life as she wanted. After almost four decades based in England, including spells in Stockport and Alnmouth, McDermid returned north of the Border in 2014.

She has settled in Edinburgh and has a home in Stockbridge with her wife Jo Sharp, a geography professor at the University of Glasgow. "The country I have come back to is not the country I left," she says.

"There has been a real shift in people's attitudes, lifestyles and the possibilities. Recently there was a survey done which indicated Scotland was the best country in Europe to be gay. That was unthinkable 30 years ago.

"I felt very much that I couldn't live the kind of life I wanted to lead. To be open, straightforward and live without interference. I felt I couldn't comfortably do that here because it was always an issue and used as a stick to beat me with."

Testament to how far things have come, says McDermid, is that Scotland is a country where the majority of our party leaders identify as LGBTQ.

"Could you imagine that at the turn of the 21st century?" she muses. "There are members of Scottish Labour back then who would have had a heart attack at the thought of the party being led by a woman, never mind a lesbian."

McDermid, who has a 16-year-old son from a previous relationship, says she has noticed the sea change in attitudes most among his generation. "It is just not an issue with them. It is part of the landscape of their lives. It is not, certainly within my son's group, an occasion for hostility or fear."

Traditional labels regarding sexuality, adds McDermid, are largely dispensed with among millennials. "I feel quite boring just being lesbian," she jokes. "I feel I should be pan-sexual or gender fluid."

The Royal Botanic Garden Edinburgh, only a stone's throw from her house, is one of McDermid's favourite places to walk and clear her head. When we meet over coffee it is during the momentary lull before the full-on madness of Festival season cranks into gear.

McDermid will be kept busy through the autumn too. In the pipeline is a graphic novel based on Resistance, her apocalyptic science thriller penned for BBC Radio 4 earlier this year.

She has been commissioned by Edinburgh's Hogmanay 2018 for a project called Message from the Skies. McDermid is writing a story, New Year's Resurrection, which will be projected on to landmarks and buildings to create a literary journey.

Then it will be on to next year's novel. McDermid has said in the past that she is "planning on being like PD James and going on writing into my 90s". That ambition hasn't waned. "As long as the ideas keep coming and they show no signs of slowing up," she says.

So, 30 years down and another 30 to go? "Hopefully, if I live as long as Phyllis," says McDermid, referring to James's prolific writing career. "Only 30 books to go. I'm at the halfway point."

One thing McDermid won't do, she says, is write a true crime novel. Before becoming a novelist, she spent 14 years working as a journalist. During that time, McDermid covered stories including Hillsborough, Lockerbie, the Yorkshire Ripper and the aftermath of the Moors murders.

It never sat well with her. "One of the problems with writing based on true crime is that you can never know what went on behind the headlines. Whatever you hear is going to be partial. You have no way of knowing if what you are assuming might inadvertently cause someone even more pain.

"A sudden violent death is a terrible thing. It is a stone dropped in the middle of your life if you are one of the surviving family or friends. I really don't want to be responsible for adding to that."

Insidious Intent by Val McDermid is published by Little, Brown on August 24. The author will be at the Edinburgh International Book Festival today and throughout August, then at Bloody Scotland in Stirling on September 8 and 9. Visit valmcdermid.com