Chic and cheerful: Marc by Marc Jacobs comes to London

Designer fashion doesn't come much more feelgood – or affordable. Carola Long explains why its arrival is a cause for excitement

Stop the press! Marc Jacobs has opened a pound shop! OK, that's an exaggeration, but there are some cute-as-a-button (and that's a Marc Jacobs gold button) lipstick-like pens for just one pound in his first Marc by Marc Jacobs shop in London, which opened at the weekend. Located on the corner of Mount Street and Audley Street in Mayfair, it's the first UK boutique dedicated to the American designer's popular second line, and the one-pound pens aren't the only wallet-friendly products on sale. There are trinkets such as heart-shaped mirrors (£3) metallic snakeskin-look key loops (£3) and wellies (£14), all with the Marc by Marc label, alongside the mens' and womens' ready-to-wear and accessories. Forget Gordon Brown. Jacobs is the man to lead us out of the recession.

Jacobs that is, and Robert Duffy, his business partner and the co-founder of their company. Duffy is responsible for the retail side of the business, and for the irresistibly inexpensive knick-knacks that are only available in Marc by Marc boutiques, making them atmospheric destinations that offer more than the UK's existing concessions. "I always felt strongly that I wanted to have items that are affordable, and mean that everyone can buy into the brand," he says, "I wanted to have a T-shirt that was, like, £22. I liked the idea of introducing a third line, but it wasn't practical in business terms - so these pieces are a bit like a third line." He adds, "I'm in the new store now, looking around, and there are books, ponchos, mirrors ... much more than just clothes and accessories. About 70 per cent of what's in the Marc by Marc boutiques is exclusive to our own stores."

Of the chic location, Duffy says, "I had been eyeing up that space for five years, since before we opened the main line store in Mount Street in 2007. I was just waiting for the guy who owns it to say yes. I love Mount Street, and the fact that the building used to be a bank." It's also one of London's most fashionable enclaves, with Balenciaga and Christian Louboutin recently opening shops there. You'll only find Marc by Marc Jacobs in the hippest of neighbourhoods; they opened up in SoHo and Bleecker Street in New York before everyone else. "We don't have the big store on Madison Avenue," says Duffy, and that's part of his plan to "recession-proof," the brand. Not that Marc by Marc doesn't look able to weather the economic storm. Duffy says that its sales make up a huge part of the business- about 70 per cent, and that 2008 was the best year yet for the line, which launched with a catwalk show in 2001.

It's not hard to see why it's so buoyant. The clothes and accessories aren't as much of a snip as the pens, but they are still affordable, or save-up-able, depending on your budget. And it's one of a handful of diffusion labels, along with See by Chloe and Sonia by Sonia Rykiel, that are priced much lower than the main lines. Without Marc by Marc Jacobs, the resolve to buy fewer, high-quality clothes, rather than mounds of cheap ones, would be much harder for many a fashion-lover to keep. And then there's the distinctive aesthetic. His clothes are like sartorial Prozac, or bubble writing; they make you smile. Like the irresistible disco classic that lures even the most curmudgeonly wedding guest onto the dance floor, designs such as shoes that resemble mice, patent cork wedges or dresses with multicoloured cloud prints - all of which appear in the current collection - charm their way into the sternest of wardrobes. Somehow, influences such as 1970s New York, air hostess uniforms, childish cartoon details such as big buttons and Peter Pan collars, candy colours, plaid-clad, preppy students, grunge, and Minnie Mouse all come together to create a recognisable look that stays the right side of cute.

Interest in the shop was already high last week before it opened on Saturday, with passers-by peering through the windows . On one day a, "very beautiful, very cool," girl came by and peeked in - looking for clothes not work-and Duffy asked her if she would consider leaving her part-time job for one at the new boutique. After obtaining the assurance that staff receive a discount, she accepted. Welcome to human resources, Marc Jacobs style.

Marc by Marc Jacobs, 56 South Audley Street, London W1, 020-7408 7050. Also available at www.netaporter.com, www.matchesfashion.com and Harvey Nichols branches around the UK, 020-7235 5000.