Asda's clothing range first made waves in supermarkets 21 years ago. Rebecca Gonsalves follows the brand's trend-spotters to New York to learn their secret

The fact that one's supermarket shopping list could now list a pair of palazzo pants alongside bread and milk is testament to the prowess of George Davies, the designer who revolutionised the landscape of affordable fashion in Britain 21 years ago.

Celebrating its milestone birthday this year, Asda's clothing range George has come on in leaps and bounds over the last two decades, not only responding to changes in how the nation shops, but driving it forward, too.

Brand director Fiona Lambert was brought on board by Davies himself when stocking clothes alongside sundry goods was a revolutionary prospect.

"At the time George started it, he couldn't actually say what he was doing, just that he had a fantastic proposition that was brand new to the market with great potential. It was very exciting to be there at the beginning – there was no supermarket fashion at all until then," she says.

As every successful brand knows, the customer is king and, to capitalise on the 19 million shoppers who go to Asda every week, George has built a brand that can be trusted to provide key high-quality basics as well as a fast rotation of fashion-led pieces.

Rather than lazily creating cookie-cutter copies of catwalk styles, the brand's designers work to translate key seasonal trends into more wearable pieces. A classic example is the cropped trousers in the birthday range, inspired by a leather Isabel Marant style from last season which had a moment in the spotlight when worn by Victoria Beckham. Knowing that red leather is far too outré for the George customer, instead ladies formalwear buyer Ruth Golightly commissioned a cotton sateen fabric, with a bit of stretch that shopping-basket analysis has proved the George customer loves.

Golightly and formal wear designer Amanda Wilkinson regularly travel the globe on inspiration trips, armed with a dossier of colour and print trend stories to keep on top of ever-changing tastes. The pair recently took a trip to New York, looking for inspiration for next year's high summer season. The first stop is the vintage boutiques of Soho where, among the classic Chanel suits, beautiful beaded dresses catch Wilkinson's eye for last minute additions to this year's Christmas collection. As soon as she is out the door, Wilkinson is furiously sketching details to pass back to the London team.

At the Hell's Kitchen flea market the rails groan with eclectic vintage pieces: tea dresses; brash Eighties florals and glittering sequins are lined up against fur jackets and silk scarves. The stallholders here are used to designers ransacking their wares for inspiration. As he takes the money for Wilkinson's purchases, one vendor with a policy of no photos explains that "designers used to buy" – he has a business to run too.

As supermarket shopping has grown over the last few years, so too has George's standalone website, ensuring those who don't shop at Asda for their groceries can still buy into the brand. Using social networking, blogging and its e-commerce site, which receives half a million visitors every week, the brand plans to double its business in the next five years – eminently achievable thanks to the brand's dedication to building momentum.

George at Asda celebrates its 21st birthday on 26 May,

Click here to watch 'Life of a garment', a video commissioned by George at Asda to celebrate Graduate Fashion Week