It remains a moot point why, of all the bizarre shopping vignettes of the past fortnight – the hordes that congregated to witness the unveiling of Kate Moss’s Topshop collaboration last Monday, the queues that formed a few days later outside Boots (Boots! For heaven’s sake) for some of the company’s rapidly running out Protect and Perfect antiageing cream – Anya Hindmarch’s I’m Not a Plastic Bag became a lightning rod for all the evils of modern life, from the vacuity of celebrity culture to consumer greed, sweatshops and the leaky, lemming-like logic of the latterday self-styled “environm-entalists”.

The 20,000 bags sold out in an hour, featured on the Today programme, had the lyrics to I Will Survive rewritten in their honour (“I was standing in the queue, I was petrified”); prompted Hindmarch, whose core constituency is affluent fashionistas, to pen her first column for The Sun; featured in four cartoons; inspired one Marissa Vanderzee to launch an alternative (“I’m Not a Smug T**t”) and helped to usher a new phrase into modern English: extreme shopping – though in nearly all cases the queuers seem to have conducted themselves with good-natured patience. Perhaps they simply wanted to be part of “history”; or possibly hopping from fashion queue to queue is the next step on from festival hopping. Still, when it was found that its cotton was neither organic nor Fair Trade, Sam Maher, of the action group Labour Behind the Label, accused Hindmarch of hypocrisy, adding that anything made in China is essentially unethical. Next month the bag is launched in the US through the Whole Foods chain. Team Hindmarch are already battening down the hatches as the hype there gathers momentum.

One might expect Hindmarch, whose press normally consists of glowing snippets on the fashion pages about butter-soft leather and hand-stitched sequins, to be either a nervous wreck or unashamedly revelling in the free publicity. When we meet on Friday, after her daily workout with Matt Roberts, she looks defiant but thoughtful. She’s been through the indignant phase. “That first listing on eBay was annoying,” she says, “but it was bound to happen. The bag was underpriced and it was always going to find its level in the market. And if someone makes £100 on eBay, then fine, have a great weekend.” Currently she’s at the philosophical stage – up to a point. “The irony is that my initial worries were, ‘Will this thing sell?’ I had visions of the bags gathering dust in Sainsbury’s.”

The decision by Vanity Fairto make it the goody bag at its Oscars party in February and the subsequent rush on Hindmarch’s London shops when it went on sale for one day suggested that surplus stock would not be an issue. But no one predicted the extent of the demand – or the backlash; some people seem to take particular umbrage at the notion of fashion trying to be an expression of anything other than rank stupidity.

“It is odd,” muses Hindmarch, “that the immediate assumption was that people must have got into their gas guzzlers to buy this bag. Or were wrapping them in plastic bags. I saw one person do that – they’d bought it as a present. I did say, ‘You can’t do that’, but . . .” she shrugs. “I’m sure the thought of getting hold of a ‘designer bargain’ appealed to some people, but I also think that people genuinely care about packaging.

“It’s the charges of hypocrisy that are really annoying,” she adds. “When We Are What We Do [the campaign group whose books Change the World for a Fiver and Change the World 9-5have sold more than a million copies between them] first approached us about doing something like this two years ago, we realised early on that organic cotton would make the project financially unviable. As it is, it’s cost us and Sainsbury’s money, because it took more than £5 to make each bag.” Fairtrade was never on the agenda. “It’s a great organisation,” says Hindmarch, “but to give you an idea of how little Fairtrade cotton is produced world-wide, when Sainsbury’s made the Comic Relief T-shirt this year it was the biggest Fairtrade order ever. As for saying that we should not have made them in China, that’s just naive. God knows I’m one of the last saddos still trying to manufacture anything in this country, but last week the factory in Northampton-shire that produces some of our evening bags went into receivership. Justin King [Sainsbury’s chairman] believes the best way to change work practices in China is by engaging with it. We shipped rather than flew the bags to the UK and hired a company that offsets the carbon emissions. We categorically didn’t use sweatshops – the factory workers who made these bags were paid double the going rate.”

Aha. Doesn’t paying over the odds wreck the local eco-nomy? Hindmarch grimaces. “It’s complicated. Like offsetting carbon emissions: who knows if that’s effective? But does that mean you sit back and do nothing?” She is not one for reclining in the passenger seat. She set up her label when she was 18: 21 years, 34 shops and five children, aged from 3 to 18 (three are from her husband James’s first marriage) later, she remains a very human mix of turbo-powered entrepreneur, shrewd designer, gifted marketer (Hindmarch’s Be a Bag, which in 2001 pioneered the use of personalised photographs screenprinted on to bags, also sold in its thousands) and guilt-ridden mother. And now, for better or worse, her lovingly nurtured niche label is a household name – just in time for the opening later this year of a large flagship on Sloane Street.

“Yeah, I see where you’re leading,” she says wryly. “But my main goal with this was not to market my name, it was always to raise aware-ness about plastic bags, about which I’m as guilty as anyone. If it’s boosted aware-ness of my brand in the process then, frankly, great. It’s only through win-win situations that you create a format that others feel tempted to follow.”

Surely there’s an inherent contradiction in preaching recycling and simultaneously encouraging people to blow £650 on a one-season “must have”? “I can see that, but weird as this may sound, I’m actually against the whole idea of the ‘It bag’. If something’s defunct after six months, that, to me, is a bad piece of design.

“That’s why I love the idea of bespoke, and of keeping certain designs in the range for years. But if you are asking, ‘Do women feel pressu-rised into buying a certain bag?’, then obviously the answer is that some do. It’s a form of security. But we charge a fair price – we’re not in the £1,000 league for something that will be obsolete by September.”

It’s easy to see why We Are What We Do, with its affirmative actions, former advertising converts and charismatic spokesperson, David Robinson, struck such a chord with Hindmarch’s brand of pragmatism: “The idea that small actions count is so appealing. There’s nothing worthy or brown rice about it; I believe that if you smile at someone, they’ll smile at someone else. There’s a ripple effect, that’s why I try to recycle whenever possible.”

But will people really remember to take their calico bags whenever they go shopping? “The most striking thing that We Are What We Do said was that when you throw something away, there is no away; currently each of us in the UK uses 167 bags a year. If we’ve made people think about that, then job done.”

The realist in her can’t help adding: “I’m not decrying the plastic bag. It’s functional, lightweight: a brilliant piece of design.”

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