Retailers are ­facing a growing struggle to keep a lid on inflation - and the future holds little prospect of a lessening in the upward pressure on grocery prices, analysts warned this week.

The latest data from The Grocer 100 pricing survey reveals that the average cost of our secret 100-item basket at the top six major multiples has soared by 4.2% over the past 12 months - well above the normal rate of inflation, which was 2.4% in July, according to official figures published this week.

At £172.85, the cost of Asda's secret 100-item basket is 2.1% pricier year-on-year, while the cost of the same basket of goods at Tesco has risen by 1.19%.

Morrisons is currently 3.42% more expensive than it was this time last year, while at £196.25, up from £188.01, Somerfield's basket is much more expensive year-on-year - despite its stated mission to slash ­prices and hone its comp­etitive edge (The Grocer, 29 April p4).

Our latest results reveal that Sainsbury's did the best job of reining in the effects of inflation. The cost of Sainsbury's 100-item ­basket rang in at just 0.42% more expensive year-on-year, which is the smallest increase of all the retailers.

Over the past five-week period, since we last checked The Grocer 100, Sainsbury's has managed to reduce the cost of its basket by an impressive £4.26. In spite of rises at Tesco, Asda and Morrisons, the latest findings from The Grocer Price Index, the survey which tracks the average cost of a basket of goods at the top four major multiples, shows that grocery price inflation actually eased back by 0.4% in the last five-week period - but this was fuelled by Sainsbury's price-cutting.

"We have continued our investment in lower prices and our sales performance continues to reflect the restored confidence customers now have in our ability to deliver great products at fair prices," said a Sainsbury's spokeswoman.

Our findings come as the Consumer Price Index, published this week, showed that annual inflation fell to 2.4% in July down from 2.5% in June. The only large upward contribution to the change in the CPI annual rate came from price ­changes for food and non-alcoholic beverages driven by upwards effects on fresh produce, milk, cheese and eggs as well as meat, where prices rose in July, especially for beef.

Christopher Gower, food industry analyst at Man Securities, said that the price increases were being fuelled by a whole host of factors and were not just down to the continuing hikes in energy, utility and rent costs.

"The effects of the recent hot weather on fresh produce items will have also had quite a significant impact on these prices," he said. Richard Ratner, food and drink analyst at Seymour Pierce, added: "Food retailers are also taking advantage at the moment to push though some price increases, and some of these will stick."