The doorstep of the world's third busiest art museum is an unlikely place to find the painter Celia Paul. Her still life compositions and three-quarter length self-portraits speak of a life spent in quiet contemplation and solitude, yet her fourth-floor Victorian apartment directly overlooks The British Museum’s courtyard as it bustles with school parties and foreign tourists taking pictures of each other on their phones. High above the madness, however, Celia’s flat remains an oasis of otherworldly calm. The late Lucian Freud bought the place for her 30 years ago when the two artists were an item and Celia has lived and worked here ever since.

Unlike many of the other flats at this covetable address, Celia’s place is modestly turned out with bare floorboards, cracked plaster and little in the way of furniture. All of the doors and corridors are spattered with paint fingerprints, while a selection of telephone numbers have been idly scrawled on the walls. Celia last redecorated the apartment in 1996 and instantly regretted the decision: “When I came back to it, all the atmosphere that had been built into the space from years of working had gone and you felt the sterility,” she says.

After making a cup of tea, Celia opens the door to the front room in which she does the majority of her painting and the instant rush of turps and oil fumes is almost overwhelming. With the blinds still drawn, the artist picks out a few recent canvases from the dozens stacked face down against the walls and places them one by one on the easel in the middle of the room. There’s a hint of ceremony to it, as she stands back patiently to give time to take in each painting: a large-scale self-portrait and several paintings of Frank, her 24-year-old son with Freud.

Born in the Indian city of Thiruvananthapuram on 11 November 1959, Celia’s parents moved back to England soon after. During her teens, her father became a warden at a religious community in Lea Abbey in Devon, an experience that she found very difficult: “I am such a private person and not only was I at boarding school where there is no privacy but at home there was no privacy and no front door, too. I think I’ve had a resistance to religion for those reasons ever since.”

In 1976, exactly a century after Gwen John’s birth, Celia left school to follow in her predecessor’s footsteps and study at the Slade School of Art. It was here that she would meet Lucian Freud, who was teaching there at the time. “I’d been very interested to meet him because I felt a connection to his work because he too worked from people who are close to him,” she says.

Faced with unknown models in the Slade life room, Celia also struggled to connect with her subjects and instead turned to the person to whom she was closest: her mother. One painting that she made of her parents and her sister Kate particularly caught Freud’s eye. “I know Lucian was quite affected by that and it planted the idea in his mind for the painting that became Large Interior, W11 (After Watteau).”

During her time at Slade, Celia began a romantic relationship with Freud, 37 years her senior, just as Gwen John had become the younger mistress of the world-renowned sculptor Auguste Rodin. “Lucian used to say to me really admiringly of Gwen that, when she was really in love with Rodin in the beginning, she gave herself up to love and didn’t paint at all,” she recalls. “I don’t think he was exactly advocating it but he was full of admiration for her. I know for my own work, I found it very inspiring to be with Lucian and I was quite the opposite to Gwen – it made me more ambitious being with him.”

Does she think that she could have given up painting if Lucian had asked? “Well, it’s not exactly a pleasure, painting. I often think my life would be easier if I…” Her sentence tails off and her face looks almost frightened at the prospect. “I can't really imagine not painting but that’s because it's been part of my identity since I was 15. It is an exhausting thing – as I get older more and more, I find it takes it out of me physically and emotionally. Sometimes I have dreamy, tempting thoughts of packing it all up but I don't know how I could really live like that.”

Spend an hour in her company and Celia’s single-minded devotion to painting is clear. There are times when she sounds haunted by her art, as though it is driving her on almost against her will at times. “It’s incredibly important to me to spend on my own and make my whole life [a part of] the discipline that goes into making the painting,” she explains. “When Frank was little, I would often come here and have to spend hours sitting without doing anything. That was very, very hard to explain to my mother because she was looking after him for me and it would have been easier [for her to understand] if I had just gone into my studio, slapped on a lot of paint, finished a picture and gone home.”

Although Frank has now chosen to follow his parents and become an artist in his own right, his mother’s absence upset him when he was growing up. “He used to say things like, ‘What’s so special about painting?’ but I think he has always understood it,” she says. Evidently proud, Celia has several of his wiry portrait drawings in frames in her corridor. “He can work anywhere. He likes to listen to music when he’s working and he draws on a sketchpad wherever he is. Maybe as a reaction to me he’s decided that he doesn’t need silence or a permanent space for himself.”

The bond between a mother and son features heavily in Celia’s other new collection of work at Chichester Cathedral. Running alongside the Pallant House Gallery exhibition, Separation will include 14 paintings based upon the crucifixion and the Stations of the Cross. “I started to think about Mary’s feelings,” reveals Celia. “There can’t be anything worse than your child dying before you do. For her to have lived through that, with all the pain and indignity of old age… It made me think that I wanted to do a series about that.”

Surprisingly, the Separation paintings are the very first works that Celia has painted from her imagination. “They just came to me, it was very exciting,” she says, her eyes widening. “What compelled me to do them was Lucian’s death. Even though I hadn’t been in the relationship with him for such a long time, there was something so truthful and so strong about Lucian that life seems quite uncertain without him.”

An edited version of this article was originally published in issue 318 of Artists & Illustrators, October 2012. All photos © Steve Pill.

Many of these works will feature in a major new exhibition of her art at Chichester’s Pallant House Gallery. Painters in Parallel will explore the similarities in style, subject matter and biography between her and the late Gwen John. “I was very surprised when I got this email from [Pallant House’s Head of Exhibitions] Simon Martin to say he’d been thinking about my work,” says Celia. “Simon’s done exhibitions at Pallant House before of groups of painters that relate to each other. He did that wonderful one of female surrealists that had Leonora Carrington in it [2010’s Surreal Friends]. I think he thinks in that way and it is quite an exciting idea.”

Linking these two particular artists is far from an original concept, however. Celia was interviewed about Gwen John for The South Bank Show back when she was still a student, while more recently the critic William Feaver made the connection between the pair in his introduction to the catalogue for her 2004 solo exhibition at Abbot Hall Gallery. Nevertheless, this will be the first opportunity for art lovers to see the other John and Paul’s work side by side. “One of the things I am hoping about this exhibition is that people won’t see it as a competition,” says Celia. “I feel that me and Gwen John might be sisters holding hands across the ages and that there isn’t this kind of competitive drive. It can be a helpful thing to have similarities and comparisons.”

On the face of it, the parallels between their life stories are remarkable. Born 83 years apart, both artists had religious upbringings, both studied at the Slade School of Art and both fell in love with high-profile veterans of the contemporary art world – all while leading very private lives themselves. Most notably, both artists also produced unique, reflective and very personal paintings of their family and their homes.

Split between two rooms at Pallant House, Painters in Parallel will include two major paintings by Gwen John that Celia says will be the “presiding spirit” of each space: A Corner of the Artist’s Room in Paris and the portrait Mère Poussepin, which she considers “probably the most beautiful painting in the world”. While Celia is clearly bolstered by the prospect of sharing a gallery with her heroine, she chooses instead to focus on the many differences between their techniques. “There is a real peacefulness in her work that there just isn’t in mine,” she says, before laughing to herself. “I think mine work is more troubled whereas Gwen never put a foot wrong, she never did a bad painting.”

Celia Paul, Five Sisters, 2009-2010, watercolour on paper laid on canvas, 127x128.3cm. Courtesy of Victoria Miro, London

Celia Paul gazes out of the window at the British Museum. Photo: Steve Pill

Celia Paul mirrors the pose of her 2012 self-portrait, Painter and Model. Photo: Steve Pill