Africa Funky Fairtrade: Bra top £25, and trousers £40, Asos Africa, from 30 April,

As fashion site Asos launches three new collections, Harriet Walker takes a look at a recession-proof shopping phenomenon

Few brands are posting a rise in sales right now, let alone an increase of almost 50 per cent.

But the online fashion and beauty site has performed consistently well throughout the credit crunch and continues to thrive, even in the face of the dreaded double dip.

Originally its success was attributed to having cornered the impressionable and trend-led youth market, whose cash was not yet tied up in mortgages or childcare and could be frittered away on faddy pieces at pocket-money prices.

But the launch of three new premium ranges this month – as well as the introduction of new high-end and niche labels with every season – is proof that Asos's secret lies not so much in budget fashion, but in its infinite variety and eminently reliable customer service.

"The launch of Asos 12 years ago was a game-changer for the fashion sector," says Caroline Nodder, editor of industry magazine Drapers. "Most retailers before that time didn't believe consumers would ever fully embrace the idea of buying clothes online. Recently, although growth in the UK market has plateaued, Asos has grown its business in international markets such as Australia, where it now has a £100m operation. It also continues to lead the pack with magazine-style online content, collaborations on exclusive clothing ranges, ease of purchase through mobiles, and quick delivery options."

The latest of these exclusive launches is a collaboration between Asos and the cult London boutique bStore, which features polka dot pyjama-style separates and aquamarine palm print T-shirts, shorts and sundresses.

"It was the perfect partner for us," explains bStore's womenswear designer Chloe Struyk, "as we're both young and creative in our offering. Where a lot of brand partnerships limit creativity in favour of commerce, with Asos we could push the boundaries a little, sitting alongside the brave buys they have from other brands."

It's a far cry from the site's beginnings, as purveyor of copycat celebrity items – the name stands for "As Seen on Screen". This has become a minority part of the business in recent years. Instead, Asos has focused on fashion in high and low budget incarnations but always with an eye on the more directional aspects. It has injected accessible fashion with a more discerning edge, although it also offers high-street brands, comfy casuals and workwear.

Two more collections launching this month are proof enough of that: Salon, inspired by a nostalgic, vintage look, and Africa, the USP of which is ethically sourced Kenyan materials. They nod to trends, but are more daring than the average high-street tastes.

"Salon is vintage-inspired yet still modern," explains Asos's womenswear director Caren Downie. "This season there are lots of sugary-sweet pastel shades, embellishment and floral appliqué, as seen on the catwalks. In Africa, we incorporate Kenyan fabrics and prints to highlight the fact that most of the collection is produced there by an organisation called Soko, who provide fair pay and childcare for the predominantly female team."

Price-wise, these collections nestle between the high-street ranges and designer brands such as House of Holland and Nudie Jeans. Asos has come a long way since it peddled imitation Wayfarers "as worn by Peaches Geldof".