Homecoming exhibition’s 25 years of portraits from Sheffield artist who was the last to paint Thatcher

The artist – who grew up in Sheffield and started out aged 14 by making a picture of Jarvis Cocker for the local star's grandmother – has set up her easel in front of heavyweight sitters ranging from politicians Tony Blair and David Blunkett to actor Derek Jacobi, and was the final person commissioned to paint Margaret Thatcher.

Now she is coming home for her first big retrospective. Titled GAZE, the exhibition at the Graves Gallery brings together more than 100 of Lorna's pictures from a career that spans 25 years - and the experience, she says, is proving 'overwhelming and moving'.

"It's a really big moment for me," she explains, highlighting that the bulk of the portraits have never been seen in the same place.

"To be able to see the trajectory of my progression and how far I've come is quite startling."

Lorna led the process of scouring her archive to choose the finest portraits for inclusion, concentrating on paintings that represented 'key moments'.

"It's almost like a diary, these visual markers of my life," she says.

Consequently Jacobi – who Lorna 'collared' outside the Crucible Theatre after finishing her art degree in 2003 – is present and correct, as is Lord Blunkett, whose light-filled portrait was sold to the Palace of Westminster where it normally hangs.

"It's the first time it's ever been shown in Sheffield. That was one I thought we'd really got to get, by hook or by crook. He was the home secretary at the time, and he very kindly sat for me which I think says so much about him and the kind of person he is. I wrote him a letter that said 'You're not in the National Portrait Gallery and I think you should be' - he sat for me and I did get the painting into the National Portrait Gallery and the BP Portrait Award."

The installation at the Graves Gallery wasn’t without its drama. When Lorna unpacked her 12ft painting of the Last Supper she spotted that Jesus – portrayed in the artwork by black fashion model Tafari Hinds – had been shot at with an air rifle in what she believed was an ‘iconoclastic act’.

“It really upsets me to think someone was so aggrieved by my portrayal of Christ that they wanted to attack it,” she told The Guardian last week.

Lorna spent much of her childhood in Ecclesfield, living in a former vicarage with her father Peter, an architect, and mother Margaret. One of her earliest memories dates from her time at Grenoside Infant School, when she and her classmates were making pastel drawings of the main character from children's book The Owl Who Was Afraid of the Dark.

"It got to playtime, the bell went and everybody went out," she says. "I remember, plain as day, asking the teacher if I could stay in and finish my picture, which I did. I kind of feel like nothing's changed - that was my happy place. I still have that picture, it was a contender for the show."

She went to Notre Dame School and Sheffield College before Falmouth College of Art and the Prince's Drawing School in London.

“I strive to capture a likeness using large expressive brushwork to convey the character and vitality of my sitter,” Lorna once said when asked to describe her style.

Jarvis Cocker appears in GAZE, but in abstract form, his image cut into pieces and rearranged like a puzzle. Lorna wanted to exhibit the more conventional picture she painted for his grandmother, but 'the logistics just didn't happen to get it in time', she says.

The latter picture came about when she met Jarvis' family at Sheffield City Hall in 1995, when Pulp played a major show on their Different Class tour.

"My friend Mary said 'Lorna's a brilliant portrait painter, she'll do you a picture of Jarvis'. After the show, bold as brass, we walked backstage, and there's his grandma. She goes 'Oh look, it's those lovely girls, they're going to paint us a picture of Jarvis, give her our address!' I did the painting from the cover of the NME. When I bumped into Jarvis about eight years ago in London and asked him about it, he said 'I have to pass it every time I go to the loo at home, it's on the landing'. That was my auspicious beginning."

Lorna painted Baroness Thatcher in 2007, six years before the divisive former prime minister's death. The giant, six feet square artwork depicts the Iron Lady gazing upwards, imperiously.

"I felt I was the only one to paint her in a way that wasn't a form of propaganda," says Lorna. "I somehow managed to get complete access without it being mediated by anybody looking over my shoulder. I wanted to do a portrait I'd never seen - that if a Martian landed tomorrow, and asked what Margaret Thatcher was like, you could point to it and go 'she was like that'. There is no way on God's green earth that the Conservative Party would've let anybody paint that portrait. All the portraits I'd seen of her were very suave and soft-focus - how she saw herself."

As it happens, Lorna's bold statement now hangs in the boardroom at Conservative head office - a monolithic icon that looms over party members.

"She had tremendous gravitas, more than just about anybody I've ever met," she says. "She was very kind to me but she had this immense presence."

Lorna is represented by art dealer and broadcaster Philip Mould, who sold the Thatcher painting for £500,000.

"He handles that side of things so I can just be in the studio painting and not worrying," she says. "I've somehow always managed to eke out the money I've had from commissions, and then doing my own stuff the rest of the time. If there's nothing happening I'll always make my own projects. Like my mum says - 'You're never short of ideas, Lorna'."

She recently painted the former Archbishop of Canterbury Rowan Williams, who needed a portrait to commemorate his time as master of Magdalene College, Cambridge. Williams previously sat for Lorna 16 years ago, and both pictures feature in GAZE.

"He remembered me, and when they asked him who he wanted to paint his picture he said 'I want Lorna to do it'," she says.

Photographs, Lorna thinks, 'don't negate the need for portraits'.

"A painted picture on a wall in a room is always going to have a certain texture and atmosphere that for me a photograph will never have. I think oil on canvas is in a dialogue over centuries, it's communicating with pictures from 500 years ago and if the world's still here it'll communicate with pictures hence. Photographs fade and they're so of their time."

Lorna, 39, lives in east London, and paints at a studio in a bid to create a better work-life balance. "I haven't always been able to do that, but I do like it. I often work really late and it's nice to be able to go to my flat and that just be an oasis of calm. In the past I'd often get up in the night, look at a painting, see something, pick up the brush and start going at it."

She hopes to carry on painting indefinitely, just like her hero David Hockney.

"He is the person in the world I'd like to paint most," says Lorna. "I absolutely love him and, like him, I have no plans to retire. He's the perfect example for everybody – in his 80s and living his best life, still making amazing art."

And the fact GAZE is happening in Sheffield means more to her 'than if it was anywhere else in the world'.

"There will be lots of people who come to the exhibition who'll say 'I remember Lorna, she always loved drawing'. I just think when people have got a personal connection with the person who's made the art it's a really nice thing. It demystifies the process a bit. Often it can seem very 'other'. I really like the idea of schoolkids coming."

GAZE is at the Graves Gallery until February 15. A study for her Last Supper painting is on show at Sheffield Cathedral while in Barnsley her portraits of cricket umpire Dickie Bird are being displayed at The Cooper Gallery from November 28 to February 15.