Shopping isn't what it used to be. Instead of popping down the local high street to see the butcher, baker and candlestick maker, we simply do a one-stop shop at Tesco. The used car business would rather like it if we did the same. Pile 'em high and sell 'em cheap. James Ruppert finds out if theory matches reality.

Up to now a lot of so-called used car supermarkets have been disappointing places. Quite often cars are parked tightly together, fresh out of the auction ring, or off the company fleet, under-prepared, scantily warranted and often overpriced.

The supermarket image of quality at a competitive price in a pleasant environment has been an illusion. However, there are now two companies determined to change the way we buy used cars.

The Car Group, and its growing The Car Supermarket chain, after recent acquisitions has become the country's largest single retailer of used cars, operating from huge sites in the Midlands and Wales.

Meanwhile, Carland began operating in January from Lakeside Retail Park in Essex with aims to revolutionise the pounds 23bn UK used car market with a chain of indoor car retail superstores.

First stop in our test is Northampton and the Car Supermarket's 10-acre super-site. Car Supermarket claims to have over 800 nearly new (up to two years old) and not so new (two to five years old) cars permanently in stock.

According to the company's chief executive, Peter King: "As with all other areas of supermarket-style retailing, the public wants to be able to choose from the widest range of goods." Fancy a Ford Mondeo? There are several rows of nearly new examples. The same goes for Vauxhall's competing Vectra. Down the scale there are Ford Escorts and Vauxhall Astras by the dozen, right down to Rover 100s, Nissan Micras and Vauxhall Corsas.

Not only is there a big choice, the cars are cheap: pounds 9,000 buys a 16,000- mile 1996 Mondeo 1.8, whereas you could pay pounds 1,000 more at a dealer. Among the prestige cars on offer which, at the time of our visit, included Mercedes and Volvos, a BMW 320i Touring at pounds 20,299 with pounds 4,000 miles on the clock would easily make pounds 22,000 on a BMW forecourt.

The situation should stay that way because the company has recently introduced its Price Pledge. This means that if you can find the same model and specification with a similar mileage, within seven days of purchase and an hour's drive of the Car Supermarket, the company will refund 110 percent of the difference.

Chris Caygill, the company's operations director, says: "Quite simply, we are doing the legwork for the customer. We run exhaustive checks of press advertising and we mystery shop competitors' sites to guarantee our prices are the best and if our research shows the same car is cheaper elsewhere, we adjust the price of all our equivalent stock the same day."

The cars come with a three-month warranty and an AA certificate confirming finance and insurance checks, mileage and previous ownership. Some cars come with two free services and MOT, but you'll have to pay for the road tax.

It's well over an hour's drive from Northampton to Thurrock, so no point in relying on Car Supermarket's Price Pledge. But it wouldn't matter anyway, because Carland are going for the premium-priced, Marks & Spencer approach to used-car retailing. Consequently the 300 cars are well presented in pleasant indoor surroundings.

Like The Car Supermarket, no sales staff will hassle you, but greeters will hand you a map. You can interact with touch-screen terminals to help you identify and then locate the cars that suit your budget or requirements.

The toilets are spotless, babies can be strapped into free pushchairs and potentially fractious youngsters can be deposited in the Cartoonland Games area. There is a cafe.

As for the cars, they are unlocked so you are free to look around, which is even easier because they are parked a sensible distance apart. All the relevant information is on photocopied specification sheets found in the windscreen mounted dispenser.

The cars come with a 30-day exchange or money back guarantee. There is a 150-point RAC inspection, one-year warranty, a year's MOT and one-year driver's insurance. If you want your old car valued, they will even clean it first. But you can't haggle about the prices. This is an all-in, non- negotiable package. Consequently, a Corsa SRi at pounds 7,500 was almost pounds 900 more than a dealer would charge and a Rover 200SLi pounds 500 more.

So why would you expect buyers to visit Carland rather than their local Vauxhall showroom? "I've never heard of someone going to a car dealer for a day out, whereas Carland is an experience for the family", says James Bidwell, marketing director.

You can expect to see more of them, too. Thurrock is the first of 20 projected stores.

Certainly there is a lot that the established motor trade could learn from Carland when it comes to presentation. However, you are paying for the privilege. So if you want a fairly new, low-mileage motor, with plenty of colours and specifications to choose from at a very competitive price, then it would have to be the lower frills offering from The Car Supermarket.

But there is still no substitute for research. The word superstore is no guarantee of good value, and often your local showroom can trounce these huge sites for price and personal service. Even though the future of car retailing is probably the supermarket set-up, the advice is still - shop around.

Carland, Lakeside, Thurrock, 0800 783 3366; The Car Supermarket, Northampton, 0990 289 227.