Focus: Primark chic - How the £3 T-shirt has taken over the high street

Yet this double-barrelled, platinum credit-carded one-time habitué of Sloane Street was desperately hoping to add yet more goodies to the 20 she had already bagged in the green nylon shopping net beside her. Caught in the act, she blushed scarlet about her "addiction" to the store's cheap chic style, and confessed that her husband thought she required urgent "help" to recover.

Yet in the same breath she could not help bursting out about the number of garments she had been able to acquire on one outing, all for not much more than £100. Such feverish excitement at Primark's thrift fashion has indeed broken through the class barriers to reach national epidemic proportions. And now psychologists have even given it a name - "compulsive price disclosure".

Sufferers feel compelled to tell friends (and enemies) just how little they spent on their Primark bargains, and the nation as a whole seems to have succumbed to the condition. Even that glossy fashion bible Vogue.

When Primark's cute little military jacket (£12) appeared on its pages next to a strikingly similar one from the high-end Italian designer Balenciaga (£1,190), stocks flew off the rails. Such was the demand that within hours the jacket had sold out and was appearing on eBay at twice the price.

Primark, now seared into our consciousness as an essential fashion destination, has been renamed Pradamark among the cognoscenti. Meanwhile, that former British essential, Marks & Spencer, has just announced the seventh consecutive drop in quarterly sales.

Primark's lightning-speed "interpretation" of catwalk creations makes a trip to one of its stores an adrenalin-inducing thrill - even if they tend to be in the scuzzier parts of town. Sequinned summer tops sell for £6, Pradaesque shrugs for £10, and gorgeous flowing kaftans for a heady £14. So what if they fall apart after a few washes? This is disposable fashion for a fast-moving, fickle world. Bling bling is boring; it is no longer cool to be a label snob.

M&S may bang on about quality, durability and ethical standards - but its voice is drowned out by the mix'n'match'n'bin furore of its competitor.

Primark - run by Arthur Ryan, a 69-year-old Irishman who wears slippers in the office - changes its stock practically daily, ensuring that no two visits are the same. M&S may be worthier, but its far more expensive stock sits on the rails from one week to the next producing about as much sartorial excitement as a trip to see a maiden aunt.

Even multimillion-pound advertising campaigns by M&S haven't stemmed the mass exodus to Primark, which relies on no-cost word-of-mouth to bring in the punters. Prada Woman wouldn't blush about being spotted in M&S, she just wouldn't go there in the first place. (And the truth is that even if she did wander in by mistake and found a handy little T-shirt lost in the acres of lilac crimplene, she would probably keep jolly quiet about it.)

The unfashionable mid-market position of M&S - once its strength - is now its greatest weakness as it becomes squeezed by the low-cost, high-speed players such as Primark from below and the individual top-end labels from above.

Today's shoppers want cheap-as-chips Primark mixed with (if they can afford it) one or two pricey but highly individual items from the upper end of the market.

This trend also means that the smaller fashion multiples with their signature looks, such as Whistles and Hobbs, continue to do well.

The "value" end of the clothing market - which also encompasses brands such as Florence & Fred and Cherokee at Tesco, Tu at Sainsbury and George at Asda - now accounts for 20 per cent of sales. Sourcing in countries such as China, Bangladesh and Turkey has helped to bring clothing prices down by 40 per cent in the past decade, and 5 per cent in the past year.

A new generation of "pravs" - proud realisers of added value - expect to pay less for a pair of jeans than a cinema ticket, less for a suit than a couple of rounds in the pub. Belatedly, M&S has introduced a "value" range, with silk ties for a fiver and a pair of socks for a quid, to tap into the trend. But with Primark announcing this week that it is about to convert 30 old Littlewoods stores into more of its own, it looks like too little, too late.

Primark

Price: £6

Label: Atmosphere

Quality: Pure cotton with nice detailing around the bust and hemline. Flattering, floaty shape and good colour.

Source: No country of origin on garment. Primark frequently does not reveal where it sources its clothes, stating only that it uses the same manufacturers as other UK retailers. Is not a member of the Ethical Trading Initiative, but says supplier factories are independently audited and that it has its own ethical standards.

Ambience and service: Bright strip lights, piles of clothes, packs of shoppers clutching huge nylon sacks for storing their bargains, priced £3 and up. General feel of a bun-fight. Customers stripping off among the rails to try on clothes. No perceptible service, lengthy but fast-moving queues at the checkout.

Durability: Experience suggests Primark garments often lose their shape and colour after a few washes. Unlikely to be still wearable by next summer, but will probably last through this one.

Marks & Spencer

Price: £21

Label: per una

Quality: 100 per cent viscose, so could be sticky in hot weather. Detailing on bust slightly wonky. Nicely floaty, but colour a little sickly.

Source: Made in Turkey. M&S always reveals the country of source and is a leading member of the Ethical Trading Initiative, with the highest industry standards on both labour conditions and environmental issues such as not using toxic or harmful chemicals in manufacturing consumer goods.

Ambience and service: Bright strip lights, acres of frumpy clothes concealing the odd clothing gem. Few customers at the checkout so no queuing, but no sense of occasion either.

Durability: M&S's in-house quality team ensures that most of its garments are easy to wash and long-lasting, with little or no shrinking, bobbling or colour loss. Would probably last until next summer, but then you might not want it to.

Whistles

Price: £44.95 in the sale, a 35 per cent reduction from £69.95

Label: Whistles

Quality: 100 per cent high-quality cotton with nylon trim. Beautiful colours and patterns, flattering tailoring with funky gold braiding and the odd sequin. Looks fabulous, great for dressing up jeans or summer skirt.

Source: Made in India. Whistles maintains tight control over its suppliers through dedicated in-house design team. Ambience and service: Bought on the designer floor of Barkers department store in Kensington. Clothes attractively laid out even in sale time, no queue at the checkout and assistant happy to put garment to one side while I continued shopping. Pleasant experience, although a costly one.

Durability: Hand-washing only or gentle dry-cleaning, with ironing also a bore because of the sequins and nylon trim. Could only be an occasional item for this reason, but if looked after well could last for ages.