Maria Grachvogel – fashion designer, working mum and the woman who famously put Posh Spice on the catwalk in a pair of green hot pants – is clearly someone who likes to take the bull by the horns.

Like now for instance, mid interview, while we're discussing the trajectory of her fashion career and how much she enjoys dressing women in clothes they love to wear. "I'd like to dress you today," she announces, as though the tight schedule – interview, photographer, lunch, then customer event at Harvey Nichols in Edinburgh before a train back to London – mattered not a jot. "There are pieces of the collection that quite frankly would work for you right now."

She's not being rude, incidentally. Grachvogel's words are more directed at the pregnancy-shaped hump on my middle than the general silhouette of my body. Still, I'm loath to agree. It's not that Grachvogel's designs aren't nice – they're quite lovely in fact – it's just that right now I'm not much in the mood for playing dress-up in an up-market department store, not when I'm in the role of oddly-shaped dolly.

Grachvogel insists, though. She's been through all this before, she says, two-and-a-half years ago when she was pregnant with her son Ansel. "I just wore a lot of draped items," says the London-born designer, who now lives in the city with Ansel and her husband Mike Simcock. The 42-year-old designer picks out two dresses from her current offering in Harvey Nichols for me to try on. The first, a floor-length red-carpet-style number with bold print, looks like it's going to make me resemble a technicolour Tweedledum, but in fact it's quite flattering. "I knew that would work on you," smiles Grachvogel. The second is a simpler grey option – with lots of draping, naturally. This ad hoc dressing-up session takes place in the absence of a photographer, but it allows me to appreciate the cut of her clothes. "There's something in the collection for everyone – I make that part of my mission."

Grachvogel says all this with complete sincerity. It's clear she wants her clothes to make women feel better about themselves – not an instinct every fashion designer has. "What we do is quite different in some ways to other designers because we think so much about cut and fit and dressing lots of different body shapes – tiny body shapes as well as curvy shapes," she says of her label, which comes in sizes six to 20. "We don't do everything in a 20 and we don't carry everything in a six. But we do have different products that work for different shapes."

Grachvogel doesn't talk like your average fashion designer. There are no off-the-wall inspiration references, no dwelling on the latest trends. Instead she concentrates on making clothes that fit a diverse range of body shapes and sizes, and is keen to point out that she also enjoys meeting customers while working incognito in her London store.

It's all a far cry from the Maria Grachvogel the public were presented with in the late 1990s (she established her eponymous brand in 1994, but it wasn't until a few years later that she became well-known). At that time, celebrity culture was at its peak and catwalk shows seemed to be as much about making headlines as showing off the latest designs.

Grachvogel's twice-yearly fashion shows were the stuff of legend. Victoria Beckham, then a regular client and friend, started the trend by taking to the designer's London Fashion Week catwalk in a series of eye-catching outfits that included those green hot pants and a slashed-to-the-thigh dress. Those images of Beckham in all her fashion glory went global, and soon after that event Grachvogel put a dress hand-sewn with thousands of diamonds on to her catwalk, garnering yet more publicity.

Then, without much warning, she seemed to disappear. Her catwalk shows at London Fashion Week ceased and her name was no longer dropped as frequently on the pages of glossy magazines. "We kept things quite quiet for a long time... there was a gap," acknowledges the softly-spoken designer, who today couldn't appear any further from that flashy world of celebrity. "I'm quite a private person and at that time I could have probably taken [the celebrity designer status] into a whole other area if I'd wanted to, but it's not really my scene.

"It depends what you want in life, I suppose, and I didn't much fancy it. I've seen from some of the clients I dress what can happen when you take that path; you're followed around London and not able to function – I can potter round London and no-one bothers me."

It's interesting, perhaps, that while Grachvogel was taking some time out, working in her store and honing her brand, her most famous celebrity client was building a fashion brand of her own. Victoria Beckham, once a fifth of the Spice Girls, is now head of one of the world's most sought-after fashion labels, one that is now better known than Grachvogel's.

What, I'm keen to know, does Grachvogel think of her former catwalk star's designs? "I haven't seen her for ages, actually, is the truth," says Grachvogel candidly. "She's a busy lady now and she's doing fantastically well. She was always incredibly stylish – very strong opinions about what suited her body and she had a really strong sense of her own personal style. More so than other clients; she was more developed.

"She had a really keen sense about cut and fit and I think that's why she gravitated towards my clothes. So it didn't surprise me when she said she was going to start her own label."

Beckham aside, Grachvogel still has her share of celebrity followers, including American singer Kelly Rowland. "We had such a strong celebrity following, which we still have actually," she admits. Although now the famous clients are spoken about less. Instead, Grachvogel wants to focus on communicating her passion for dressing women well – a passion, she admits, that hasn't always appeared obvious in the past. "This time round having had the experience from before I realised how important it was to build the company's identity and for people to understand the reasons why I was doing what I was doing."

Which brings us neatly to the reason why Grachvogel, in the midst of media, celebrity and commercial success, shut up shop at London Fashion Week and disappeared from the public eye. "It just all got a bit too much doing the shows, so I decided it was a choice between doing shows and learning about retail. Having that whole thing, the shop, meant so much to me that I invested my time in learning that. It was just a choice."

A few seasons ago, Grachvogel, pleased with the progress she'd made on the retail side of the business, decided to return to the catwalk. This time there have been no celebrities strutting their stuff.

What about putting so-called "real women" on her catwalk rather than models? Grachvogel is unconvinced. "Putting real women on the catwalk seems like a gimmick," she shrugs. Yet there's no doubt that real women are at the heart of everything Grachvogel does. Her trousers – called "magic pants" because they seem to flatter so many different figures – attract customers in their droves.

Flattery is an inherent part of Grachvogel's designs, whether that's through the cut of her dresses or the prints she creates to enhance a woman's figure. Her clothes, though often spotted on the red carpet and now increasingly featured in fashionable magazines, are not about seasonal trends but instead wearability.

She insists that's always been the ethos of her label. "It probably all started when I was about 12 or 13 years old. At eight I was saying to my mum that I was going to be a fashion designer. At 12 I started cutting and sewing, and it was about that age I started to get quite fascinated by cut and fit and sizing because it became apparent to me that I was a different size in every shop I went into.

"I started measuring everyone – I started measuring all my friends and asking them what size they fitted. What was really interesting about that was that one person was a size eight and another person was a size eight too, but their measurements were totally different. I became quite interested in that and also in my own body shape. There were certain things when I put them on I didn't feel good in, so I started making myself garments that made me feel taller, slimmer."

Grachvogel says that's how she still designs – trying samples on members of her team to see how they fit different shapes. She adds: "That way you end up with a garment that fits more women better and that is going to make women feel better. That's really the mission statement of our brand."