Asda is “still the reigning champion” of cheap grocers despite prices soaring 6.3 per cent in the space of a week.
Consumer website alertr said the leap, in early September, was the steepest of any British supermarket.
Its analysis pitted Asda, Tesco, Sainsbury’s, Morrisons, Waitrose and Aldi against each other, but did not include discounters.
Price changes – especially dips – were apparently most common around the middle of the month.
Morrisons saw the sharpest decline, with prices falling 4.4 per cent in the week from September 10.
The average basket at Asda, which ranked behind Aldi and Lidl in a similar test by Which?, cost £108.72.
Sainsbury’s was labelled “one to watch” as it surged into second place with £113.34.
Tesco missed the silver medal by just 58p, while Morrisons (£117.54) and Ocado (£122.57) finished in the bottom half of the table.
Waitrose brought up the rear with £126.77.
Despite recent reports of food shortages, alertr noted that none of the 42 items it compared had been out of stock.
“It is interesting to see that the six supermarkets have stayed in a similar price order to previous months,” alertr founder Andy Barr said.
“Dropping their prices, Sainsbury’s are becoming one to watch as they have stolen second place from Tesco, who was regularly second most cost-effective earlier in the year.”
He added that there was a “relatively large difference between the top and bottom spots on the leaderboard of £18.05”.