But one supermarket has been conspicuously absent from the organic revolution. Marks & Spencer has trailed the other supermarkets for more than a decade, having dropped organic lines after a lacklustre trial in 1989. Now, in a jaw-dropping U-turn, M&S is about to spend millions trying to make the chain "Britain's leading organic grocer".
It has even appointed Bartle Bogle Hegarty, the innovative advertising agency responsible for the Levi's campaign, to market its winter food range.
M&S means business. Walk into any of its food stores and you are met with evidence of the firm's new-found evangelism. The mouthwatering giant photographs of St Michael's latest food lines have been replaced with bold placards reading simply "organic produce".
All good strong evangelistic stuff. But will the customers buy enough to make this sudden conversion worth while? Early signs are positive. "When we introduced our first organic sandwich - tomato and cheese - our phone line was inundated with customers saying they were delighted but wanted more types," says Maya van Eerde, the store's press officer.
M&S buyers have set up consistent supplies of organic food, enabling the chain to offer 50 lines. By the end of this year M&S expects to have 100. New organic products will be a feature of its autumn food range, with an emphasis on organic versions of M&S staple foods such as shepherd's pie and sponge puddings - the feelgood props for millions of harassed, stuck-for-time shoppers.
M&S's organic policy (or lack of it) until now has been a classic example of how not to do it. Its first error, based on complacency, was to underestimate the effect that a series of food scandals (most notably BSE) would have on the way consumers shopped. The second, related error was to overestimate the faith that shoppers had in the St Michael food brand. Over the years, M&S seemed to have built a reputation for selling superior food. Many shoppers did believe, correctly or incorrectly, that an M&S Battenburg cake was better quality than a Mr Kipling or a supermarket own-brand equivalent. Perhaps the chain thought this image would insulate it from plummeting consumer confidence in the food sold to us. In both respects, M&S miscalculated.
Already wounded, M&S initially made the even bigger error of dismissing public concern over GM food, something it had in common with all the large food retailers (except Iceland, which took it upon itself in early 1998 to boycott GM ingredients and derivatives in its own-brand foods). Last year M&S stated that GM food was "simply not an issue" for its customers (an uncomfortable echo of its 1989 assertion that there was "no demand" for organic food).
So by May this year M&S had embarked on a mission to restore confidence, quickly preparing its climbdown by reinventing itself as the store that "puts customers first".
It is easy to be cynical about the chain's motivation in ditching GM food, but that would be to ignore the genuine exercise undertaken by M&S. It reviewed its catalogue of 3,500 foods for GM ingredients, checking over 5,000 individual ingredients and changing 1,800 recipes. In an attempt to regain its pre-eminent position for what consumers see as "quality" food, it has pulled the plug on GM food. This makes good business sense. An association with GM food is now widely seen as a liability.
By contrast, retailers with a big organic portfolio are attractive to shoppers, significant numbers of whom have latched on to organic food as a "safe house" in a world of tainted technofood. By the end of this month, both Sainsbury's and Tesco will stock around 500 organic lines, with Waitrose at 430. Even retailers like Somerfield and Asda, which service the budget-conscious market, are extending their organic lines.
But all other supermarkets still stock branded foods that cannot make GM-free claims. M&S's unique selling point is to steal a march on competitors and declare it is the only large chain that can guarantee shoppers GM- free products, with a strong organic portfolio.
"Our aim is to offer customers the possibility of buying everything they want for breakfast, lunch, dinner and, of course, afternoon tea from our organic range," says Ms van Eerde.
As M&S shoppers stock up this autumn on organic everything from ready- made lasagne, macaroni cheese and pizza through to teabags and Madeira cake, Lynda Brown, author of The Shopper's Guide To Organic Food (Fourth Estate, pounds 7.99), thinks that the chain's new strategy could pay off handsomely. "There's no doubt M&S is the brand leader in high-quality ready meals," she says. "Its org-anic range is bound to be a winner because it gives you all the convenience and quality you expect from M&S with the additional organic guarantee. M&S may be just another Johnny-come-lately to organic food, but it is coming with a vengeance."
Marks & Spencer could hardly have chosen a better advertising agency to promote its new image than Bartle Bogle Hegarty. "They have a reputation as the most creative British agency," says Alex Fynn, the former deputy chairman of Saatchi & Saatchi. Indeed, it was at Saatchi's that John Hegarty learnt his trade before leaving in 1974, eventually to set up BBH with John Bartle and Nigel Bogle. "He is very straight, very imaginative and he doesn't have a big ego, which enables him to take a more pragmatic view of the client's needs," says Mr Fynn. BBH's experience of marketing retailers includes work for Asda. More famously, it brought us the steamy commercials for ice-cream maker Haagen-Dazs. But BBH's greatest coup was to unleash Nick Kamen's torso on an unsuspecting public in the first of a series of impossibly successsful ads for Levi's. That campaign tempted Leo Burnett, the American agency, to buy a 49 per cent stake in BBH two years ago in a deal that enriched the trio by pounds 30m. The challenge of selling M&S's winter food range will be spiced up by the lure of winning the retailer's entire account. M&S is choosing a new marketing supremo whose decision it will be to appoint a house agency.