Not like this, though. Not with the San Francisco sourdough, the pain au levain and the garlic bread with soft seams of caramelised cloves, the boule de meule, the croissants and tarts, and white crisp-cumulus piles of meringues which make it a place of knee-weakening, mouthwatering wonder. Along with the bread and patisserie, it serves coffee mostly to people who make up one of the wealthiest sections of the country. The idea is that before too long everyone will be able to buy their loaves, especially the sourdough.
Sourdough is not, though, everyday bread. It takes more than a day to make, it costs more than most people are prepared to pay for their daily bread, and it keeps for up to a week. Dan Lepard, the consultant baker to Baker & Spice is one of a crack corps of artisan bakers who specialise in sourdoughs and is instrumental in raising its profile.
In Baking with Passion, co-written with Richard Whittington and published last month, he puts the case for baking it at home (and to those without the time, an even better reason for buying it).
It is a traditional food, a dense, chewy, tangy-tasting bread made not with commercial yeast, but with a naturally fermented starter dough that creates conditions whereby wild yeasts can flourish. This raises and ferments the dough, which is proved twice before baking.
How paradoxical that the rich once valued softer, more refined bread, while the poor had to eat coarser, chewier - but probably more nutritious - loaves. Now supermarkets sell highly refined, mass-produced bread and local craft bakers are going to the wall. But there is a growing appreciation of traditional, unrefined artisan loaves.
Which is why Brigette Hardy, Sainsbury's product innovations manager, approached Baker & Spice. Early next year the firm's sourdough will appear on bakers' stands at the Fulham Sainsbury's store. Shortly afterwards, three of its sourdoughs - San Francisco, olive, and rosemary and potato - will be sold at up to 50 branches. These will be made in exactly the same way as they are in the cramped basement bakery and 100-year-old ovens in Knightsbridge, but in a newly built bakery just a few miles away on a west London industrial estate.
It is a massive investment for the owner of Baker & Spice, Gail Stephens. She opened the shop three years ago having begun as a bread broker, buying the best from various bakers and selling a hand-picked range to restaurants. Her business now encompasses the Baker & Spice shop, a factory and distribution arm supplying top London restaurants, and the new bakery which, when it's up and running, will be able to produce 2,000 loaves a day for Sainsbury's.
At the same time she is opening, in January, a second small bakery shop near her home in Queens Park, north London. Although she admits she can't bake to save her life, the mission she shares with Mr Lepard is to make real bread as widely available as possible without compromising on quality. Does this mean sourdoughs like theirs could be the next ciabatta? "No," she says, emphatically. "It takes too long. Bakers don't have the skills or the patience. Modern bread is made so fast the natural enzymatic process does not take place. You're eating an unripe product."
Breads flavoured with sun-dried tomatoes are, she says, "well and truly finished. I'm into basic bread with character". Ms Hardy at Sainsbury's shares her view. "No more bits," she says, "we want the flavour of the bread itself." And sourdough certainly has that, thanks to the natural yeasts and long fermentation. It carries on maturing and changing character, and is even best eaten when it's at least 24 hours old.
At the same time as Baker & Spice's sourdoughs are about to break through to the supermarkets, 200 miles to the north a third- generation baker is about to double his output of traditional, artisan loaves. Michael Hanson studied accountancy before he returned to the craft that was in his blood. But he realised he couldn't survive as a traditional family baker, so taught himself to bake rustic European breads, and four years ago started Carriages Continental Breads in Bradford.
Mr Hanson now has a shop in Bradford's Wool Exchange selling nothing but bread and patisserie - no distracting bottles of olive oil or preserves in pretty jars - and supplies many of the best restaurants in Leeds and Manchester and about a dozen top shops including Harvey Nichols in Leeds.
His new bakery has an oven five times as big as the one he's just moved from. From 60 different doughs, he produces loaves such as French pain de campagne, Italian country bread, Normandy cider bread, German rye, Danish saterbrod, focaccias, and old-fashioned English cottage loaves.
Some, such as an organic wheat loaf made with Breton seaweed, and a Canadian flax seed bread, are unique to Carriages. He too resists adding extras to his bread. "The finest loaf is the purest: just flour, water and salt. The flavour should be inherent in the dough."
He adds: "Bread is so undervalued. It's an essential of everyday life, yet few people care about the quality of it." He does, of course, and with Mr Lepard and a score of other like-minded bakers, he has helped set up the British Association of Artisan Bakers. Its members are dedicated to proving that real bread is not a luxury, and that there is an alternative to the over-refined, tasteless mass-produced loaves that make up the bulk of supermarkets' sales. "Everybody deserves a chance to buy a really good product," says Ms Stephens. Next year, those who can't get to Bradford or Knightsbridge will have it.
Baker & Spice, 46 Walton Street, London SW3 (0171-589 4734). Carriages Continental Breads, The Wool Exchanges, Hustlergate, Bradford, West Yorkshire (01274 744114) `Baking with Passion', by Dan Lepard and Richard Whittington, published by Quadrille, pounds 18.99Reuse content