If there is one overriding theme that comes over powerfully when talking to Mary McCartney it is how strong a bond of love and respect she had, and has, for her mother Linda. The late American photographer and businesswoman and her husband, the former Beatle, Paul, famously had one of the most enduring love affairs of modern times: she was the proverbial great woman standing, if not behind, then beside, a great man.

But what is abundantly clear from speaking to the couple's daughter, Mary, 38, is that behind both was an uncommonly close and loyal family, a closeness that remains. Earlier this year, to mark a decade since Linda died of breast cancer, Mary and her father unveiled a retrospective in London of Linda's work, which the pair had been working on for three years. Right now, the whole family, including Mary's fashion designer sister Stella, are closely involved in revitalising the Linda McCartney vegetarian food range, something Mary describes as "a very personal project".

In addition Mary, now herself a respected photographer, has become a strong advocate of good cancer care. So when she was approached by Maggie's Cancer Caring Centres to take photographs of famous Maggie's supporters wearing striking, new designer T-shirts, she was delighted to lend her support. The photographs, being published for the first time as part of The Herald Friends of Maggie's campaign, feature celebrities including the actress Amanda Holden, and the singer Sophie Ellis Bextor pictured with her mother, the former Blue Peter presenter Janet Ellis, whose friend Caron Keating died of breast cancer in 2004.

Coming together for the photos in the new London Maggie's centre gave McCartney the chance to spend time with staff and patients. She found the whole experience "truly inspiring" and believes her mother would have, too.

"I think she would have loved it," says Mary emphatically. "It feels like it's been designed to keep everyone's spirits up, which I think she would have liked." Thinking about her mother's period of treatment, she recalls strip lighting, a lack of windows and a distinct hospital smell, which Maggie's avoids: "It isn't dull, dark and depressing. There's glass, wood, colour and daylight, it's very open plan. It didn't feel oppressive. It's a real contrast to hospitals - you can allow in so much air and it doesn't have the smell. You walk in and it feels like a well-designed space."

Another factor that would have appealed to the redoubtable Linda, she says, is that it is well run. "I think she probably would have appreciated the organisational aspect of it - it doesn't feel flaky."

When Linda McCartney was diagnosed with breast cancer in 1995, it was Mary's first experience of cancer at close hand. Her head was full of questions about this bewildering new visitor to their lives. "It's like learning a new language - chemotherapy, radiotherapy, all the different medicines. It can be very daunting," she says. So the fact that Maggie's centres provide support and information to the families as well as the patient, deeply impresses her. "It's so important. I find that it's the kind of illness where there are always so many decisions to make.

"The day I was at Maggie's, there was a husband there with his wife, collecting the medication for the week, and he was having a consultation with one of the counsellors. He said he saw a counsellor each week. I think he really benefited from it as well. They can help give you information so you can feel more confident about moving forward.

"That's why I feel quite strongly that there should be as many of these centres as possible because they're such a great help to people."

A loving family is a great support and the McCartney family were certainly that. Mary has an elder half-sister from Linda's first marriage, Heather, who was adopted by Paul; a younger sister, Stella, the fashion designer; and a younger brother, James, a musician and songwriter. The family adopted a low profile during Sir Paul McCartney's recent divorce from Heather Mills, which generated weeks of headlines. "I wasn't really surprised by the amount of coverage but I definitely kept out of it. I didn't read a lot of it," she says. Mary herself has two sons from her marriage to producer Alistair Donald and is expecting her first child with film-maker Simon Aboud. In fact, as we speak she is a weary nine-and-a-half months pregnant.

As a parent, she believes she has taken a lot from her own upbringing, such as "giving my children a sense of freedom, encouragement and adventure, which I got from my parents". Family holidays in Argyll were central to that. "We'd spend August up there. I kind of feel as if I grew up there," she says. She recalls driving up from the south of England in the summer, past mountain springs, looking in amazement at remote crofts and wondering what the occupants did when they needed a pint of milk. Her experience of exploring for hours and "being a bit feral" is deeply etched.

Has she come to Scotland recently? "I haven't as much since my mum passed away but I'm starting really to get a craving to go again now," she says. "I think we all stopped for a while because it felt a bit weird going up without her, but now it's kind of time to start again."

One of the projects that has been occupying her and her family recently has been "revitalising" the Linda McCartney vegetarian food range, which was launched in 1991. Mary had helped her mother with both her cookbooks and food range. Last year, the firm Hain Celestial bought the licence to the foods and the McCartney family (who are all vegetarian) have since been working with the firm, not only with photography and packaging design, but with new lines. "We're working with them now on coming up with ideas based on the recipes that mum had and the way she cooked. We're very hands-on. We want to do it for her, the way she would have wanted it done."

Mary's photography, too, is in a sense a tribute to her mother. Linda Eastman McCartney photographed stars such as Jimi Hendrix, Bob Dylan and The Doors. When Mary decided to become a photographer too, Linda was thrilled. "She was really happy, really pleased," says Mary, with a smile. "If I'd had a day taking pictures, she'd go how did it go? When do you get the contact sheets back? Phone me the minute you get them back and come down and we'll go through them.'" While McCartney does a lot of fashion photography, which is a more formal style, she definitely sees similarity between her and her mother's styles when it's just her and her camera.

Her eye for fashion has certainly been caught by the new Maggie's T-shirts, exclusively designed by Dandy Star. The colourful T-shirts each bear one of three words, "hope", "joy" or "be", chosen to represent the ethos of Maggie's; McCartney says they made her job as a photographer easy. "They're great; often charity T-shirts are things you love because they're for a great cause but these are ones that a lot of people would want to wear anyway. They're bright, simple and they've got good typography on them; they're not filled with logos."

She hopes her photographs promoting the T-shirts will encourage more people to support Maggie's: "It's just a really really important organisation."