OH ME oh my, a little frisson sings out as I exit the subway at London’s Kensington High Street, headed in the direction of Lulu. Why? The singer forces a range of questions as long as an double LP track list.

We think we know her because she’s been around longer than the Hit Parade, this small strawberry blonde with a boom-bang-a-bang voice that can also melt frozen hearts. We know she won Eurovision with a naff song (although she later admitted she’d have sung Baa Baa Black Sheep if it meant good TV ratings). We know she loves Scotland because she invokes her Glasgow east end roots as often as the 41 bus runs through Dennistoun.

But here’s what we’ve never been sure about – in her heart is she more Alexandra Palace than Alexandra Parade? Is she really as tough as the steel needle on your granny’s gramophone as her ubiquity and longevity suggests? Was she happy to abdicate her position of Britain’s soul queen to become a Saturday night variety telly jack of all trades?

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There are more questions – she’s written the soundtrack for the new Robert The Bruce film starring Angus Macfadyen. Does she have a fervour for independence? And what of her work rate (Lulu has just finished a 40-date tour with Take That). Will she die without the spotlight shining on her (incredibly well-preserved) 70-year-old face?

The frisson, however, has emerged from knowing the singer is more guarded than the Waleses’ children when it comes to interviews. What’s a good in? While walking the High Street, there it is – a poster for Elton biopic Rocketman. Reg Dwight’s tale is a story of young man feted and fawned over, thrust into an international spotlight, a creature who loses his old name, his old life and sense of reality as he becomes institutionalised by the likes of his Scots manager John Reid.

Little Marie Lawrie was just 15 when she was airlifted to London, to live with her manager Marion Massey night and day, while being controlled, Pygmalioned for success (if this were to happen to a young girl nowadays, social services, at the very least, would be involved). Can she relate to Elton’s story?

I’m now in the living room of an elegant terraced house. Lulu is sitting on the couch dressed in black from head to toe; baseball cap, trainers, jeans and a curiously thick jumper, given it’s 24 degrees outside. But she’s not alone. Christ, we’re having a threesome because on the chair to the right is her brother, Billy Lawrie (a songwriter and singer in his own right, with credits such as I Don’t Wanna Fight, for Tina Turner). It’s a worry. Interviewing two people usually results in half an interview.

Yet, Billy’s appearance is relevant; he’s a co-writer of the music for the Robert The Bruce movie. And before the Rocketman parallels can be suggested, we talk 14th-century biopics. How did Lulu (and bro) come to be involved? “Well I’ve known Angus for a long time,” she offers. “He was amazing in Braveheart [in the same role] and he called me 18 months ago and told me the film was being made. He then asked me to, well, I can’t remember the detail, but the result is we’ve written the music.”

Why the connection with Mcfadyen in the first place? Billy smiles over at his big sister, a smile which suggests “spill the beans”. “Angus and I had a relationship a few years ago,” she says in slightly coy voice. “And we’re still really good friends.”

Lulu and Billy loved the script. Lulu says she loves the fact it’s told from a mother’s perspective. “I have a son. [Jordan, from Lulu’s marriage to John Frieda]. This is about a mother’s loss.” Billy agrees: “Lu’s right about that. This script reduced me to tears.”

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Lulu suddenly springs up from the sofa and adds in loud voice: “This film is about being Scottish, being full of fire!” Does this suggest a burning in her soul for independence? She sits down and reflects. “All I can say is I’m not a political animal. As for the likes of Brexit, I have no idea what is going on. Who does? But if the Scots decided to leave the UK, well, maybe right now is the time. I wouldn’t be able to vote however, but I can hear and feel the passion.”

I can hear the Scots accent emerge as she becomes animated. Lulu, you learn, doesn’t do ordinary speech. She’s either sotto voce, very precise, or singing from the heavens. But now that we’ve covered The Bruce, what about Rocketman? Has she seen it? “Twice,” she beams. And does she relate to Reg Dwight’s chameleoning into Elton? “Yes, it’s not normal,” she says quietly of the life of change. “You know, Elton and I weren’t so close when we were younger. [The pair met before Elton wrote a Eurovision song for Lulu in 1968, which didn’t make the cut.] But we have become really close as we’ve gotten older and a lot of that is because we identify with our personal struggles and successes. Our journey in fact.”

Lulu has had her diva moments but she never became a cocaine and alcohol Olympian as did her chum. She ponders. Billy offers an encouraging smile, and the fear of the third person in the room dissipates. “A lot of my childhood was performing the role almost of parent, to my brother and sisters,” she offers. Lulu’s grandfather had been in and out of prison. Her dad Eddie, a meat factory worker, was an alcoholic and her mother, Betty, had been “disposed of” (as official records list) to other families because her parents couldn’t cope, which left Lulu’s mother with emotional issues. Lulu’s parents had a volatile, mutually abusive relationship often fuelled by drink. In short, Lulu and Billy’s home was a war bunker.

“I had a fear of losing control because I felt overly responsible,” she says of her siblings. “So if I didn’t behave, if I didn’t bring in the money and wasn’t successful, everyone would suffer.” She adds: “I think I’m quite a courageous person but I’ve had a lot of fear to work through. The truth is I’ve been to hell and back.” Billy (18 months younger) nods in agreement: “Lu was more of a mother to me than my mother. And my best friend too.” His look towards his big sister is one of solemn thanks.

As he speaks, Lulu leaps off the couch and is standing, projecting to the back of the room. “I can just hear people say, ‘What does she have to complain about? She’s had huge success’. [Lulu is reckoned to be worth £20m.] And you know, my mother would have said exactly that. But here’s the thing. I moved to London and I didn’t fall over. I kept going and the experience made me move forward.”

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Yes, you bailed the family out. But what of being uplifted to Holland Park, living with a strange adult? “It would never happen today!” she yells. “People would wonder what they were doing with me. But the truth is it was very pure.” Yet, she was separated from family. Normal life? “I used to cry myself to sleep every night. But did I go home? No. That’s the interesting thing. I’m not saying I don’t have all these insecurities and I’m not vulnerable. But I’m strong enough to ... to put it in a box.”

Lulu’s personality had been formed by Dennistoun and singing in a band as a 12-year-old. But what if she hadn’t been discovered by Massey in a Glasgow club? Would a different character have emerged? “It goes deeper than that,” she says with a sigh. “Being a success at the age of 14 means it’s very hard to mature. There’s long been the belief that those who are successful at a very young age remain at that age. So I have struggled a lot with ...” Identity? “Uh huh,” she says, in a reluctant tone. “For example, people have said I’m English.” Her voice goes up an octave. “No way! And my Scottishness comes right out when I’m with my brothers and sister. Then you go back to who you are.”

Lulu’s life, it seems, has been about permanent adjustment. Has it been about keeping Marie Lawrie locked in a cupboard under the stairs in Garfield Street only to be let out when Scottishness is revisited? “Yes, I could adjust. Marion would often say I had the resolve to work, even when I was sick, that I could switch on for kings and queens.” Her voice softens. “A lot of people say I’ve had success because I have a special talent. But lots of singers have talent. However, most would have gone home and said ‘I’ve had enough’. I was terrified of the1960s, but I knew this was my destiny.”

She could have gone home after the success of Shout in 1964. The next three singles were flops. But how does a 15-year-old deal with incredible adulation – and then drifting until 1967 when Neil Diamond’s The Boat That I Row brought her back to shore (followed by the immaculate To Sir, With Love)? “It was tough,” she says, with massive understatement in her voice. “It was really tough.”

There was some fun along the way of course. Lulu had early flings with the likes of The Monkees’ Davy Jones (who broke her heart) and the Hermits’ Peter Noone, who would drive up to Glasgow to see her. (“He’s a lovely man.”) Later, Lulu “hooked up” with Bowie, in the modern sense of the word. Billy, now the teasing little brother, chips in, smiling: “You had crushes on lots of guys, Lu.”

Lulu agrees in excited voice. “Oh my God, yes. Scott Walker. I was heartbroken about Scott Walker, whom I fell in love with when we were on tour together. I used to stand panting at the side of the stage.”

Were there ever any #MeToo moments? “I can remember one boy whom I met on holiday and he took me out in his car and tried it on. He was shocked when I said I wouldn’t go all the way with him. And he wanted to marry me!

“But usually, Marion would be everywhere. There was always someone around.” Does she wish she’d had more boyfriends? “No!” she yells. “Why would I? There are some I wish I’d had as a boyfriend, but not more.”

What of female friends? Lulu wasn’t close to the female pop stars of the day, but she did have a special affinity with Dusty – two white soul singers of class. Did they meet for coffee? “I was not the kind of person who wold call someone up and go for a coffee,” she admits. “I’ve never been a woman who lunches. Never. I still find it hard.” A posh Scottish voice emerges. “I’m not the sort to meet the girls with their handbags and shoes ... the girlfriends I have are not about shopping. We’re about substance.” He voice becomes louder. “I’m about planning. And I don’t have an army of friends.”

Is there anyone who makes her heart go boom-bang-a-bang-bang? She laughs. “No, I’m happy on my own. I’m not looking to live with someone. I was needy of that when I was younger. [That’s partly why she married Maurice Gibb.] I could feel lonely when I travelled. Not now.”

Marion Massey gave her protégé a long-term, lucrative professional life in Saturday night television but it killed off the dream of becoming the Scottish Aretha. Does she have regrets? Billy leaps in. “Her heart wanted to sing. Didn’t it, Lu?” Lulu flops back on to the couch, a metaphor for her surrender at the time. “I trusted Marion to have my back. Yet, I had years of saying to record producers [Scottish accent, wee girl voice] ‘Please, I don’t want to sing I’m A Tiger.’ And let’s not even mention Boom Bang A Bang Bang. But I was contracted to do it.”

So what would have happened had she remained in music? Interestingly, she doesn’t argue she could have become a white Aretha. “I tell myself I would have ended up the Scottish Janis Joplin. Dead. You see, I’m Scottish. My father was an alcoholic. You’re in the music business and you’re in god-knows-where. And you’re lonely. But who knows?”

As well as coping with a career that was in many ways a capitulation, there was personal tragedy to contend with, two failed marriages, the death of Maurice Gibb. “I’ve had a lot of pain. Personal struggles.” Yet, if the central theme in Rocketman is of Elton blaming the world for his woes – his mum, dad, manager – that’s not even a subplot in the Lulu story.

“I’ve looked back and blamed people in the past. I never trusted anyone. And there have been times when I’ve struggled with something, I’m about to blow a fuse, but it never did me any good, so no more.”

How did she move on? “I read every self-help book there is to read. I’ve studied Yoga sutras, so many ancient works to find the tools to help me accept things. I’ve learned not to have regrets and sit and moan about the past.”

Billy smiles and nods in agreement. He’s also followed this route to calm. His big sister continues: “I never went to school, I didn’t go to university. I never learned to debate. I’ve had to learn that acceptance is a huge feature in learning. That you can’t control others. When you realise this you can move on.”

Disappointment, she has learned, is relative. “I may be disappointed about a record not coming out or whatever but how does that compare to someone losing their house or their family? The only thing that’s important is love. I’ve had to learn that if I feel I want to punch someone, I need to feel compassion, to try and understand what they’re going through.”

That’s refreshing. But Lulu is still compelled to work. “I loved the Take That tour,” she says in excited voice. “And the boys said there wasn’t one night I didn’t deliver.” She stands and reaches up to an imaginary rope: “There’s always been something pulling me.” Billy joins in. “She has to perform, to do everything perfectly.”

Lulu squeals: “And I’m 70. And I’m going to tour soon [smaller intimate gigs] and talk about things I’ve never talked about before. I’m going to have pics of my life. I’m going to tell the stories behind the songs. And there’s more. I have three acting jobs to consider [including a classic theatre piece].” She adds: “I may be scared sh**less but I’m up for them.”

Billy Lawrie seems a genuinely nice bloke. His big sister is funny. Intense. Loud. Soft. A little brittle. And vulnerable, yet tougher than a Baptist preacher’s argument. But you sense she’s still searching – seeking validation? “Maybe a psychiatrist once said to me, ‘You will never be fulfilled. You will never be happy.’ But the truth is I have never been happier that I am now. I’ve found peace.”

Totally? Do you mean to say a film of Lulu’s life story (I’m A Tiger?) would reveal a woman who feels validated, Lulu? “Maybe,” she says softly. “I really don’t know.” Her Scottish schoolgirl voice returns and she grins: “The truth is ah’m still waiting to be discovered.”

Robert the Bruce is in cinemas now.