Asda remains the retailer with the lowest prices but is having to work harder than ever to retain its pricing crown. The big four have responded aggressively to the economic downturn, with Tesco launching its discount brands, Asda reducing the price of its Smart Price range and Morrisons running high-profile promotions. Even Sainsbury's has urged consumers to switch to own label.

This has made the pricing race far fiercer. In the second half of last year, Asda was the cheapest retailer 20 weeks out of 27. This year, Asda was cheapest in 18 of the 28 weeks, Morrisons was cheapest for six weeks, Tesco for three, and Sainsbury's for one. The price gap between the average baskets has closed, too. Asda’s average price of £54.88 was 92p cheaper than second-placed Morrisons’. This time last year the typical gap was £1.14.

The gap between second and third place widened, however, Tesco’s basket coming in at £56.76, 96p more expensive than Morrisons. Last year, Tesco’s basket was just 76p more. Sainsbury's came fourth with an average price of £57.58 and Waitrose brought up the rear as usual at £64.33.

Asda may dominate on pricing, but still has something to learn from its rivals on service and availability. On availability, Sainsbury's has achieved a real coup: last December, Sainsbury's was in fifth place with just 96.28% of products in stock. This year it took top spot with 98.21% availability and eight full baskets. Morrisons fell to second despite boasting almost identical availability to last year at 97.82%.

Availability was down on last year at the other three retailers. Waitrose retained third despite a fall in availability from 97.38% to 96.99%. Asda dropped from second to fourth after a fall in availability from 97.40% in 2007 to 96.88%, while Tesco fell from fourth to fifth with 96.27%.

Waitrose has won the top store award for service the most times over the past six months, its eight victories pipping Morrisons and Asda. Waitrose had also notched up the most service victories in the second half of 2007.

The bad news for retailers was that average time spent at the checkout rose almost everywhere. Though Asda shaved two seconds off its time to six minutes two seconds, moving from last place to fourth, the average checkout time at Morrisons rose by one minute two seconds to six minutes 24 seconds, putting it in last place. Tesco moved to first place despite the checkout taking seven seconds longer than last year, Waitrose slipped to second and Sainsbury's rose to third despite the checkout taking 21 seconds longer.