Shoppers have had less reason to buy seasonal food and drink for barbecues, resulting in a fall in the average number of visits to most major supermarkets compared with the same period last year, the information provider said.
Mike Watkins, senior manager for retailer services at Nielsen, said the rate of growth for the month to August 8 was the lowest for two years.
Watkins added: “Aside from the drab weather and the seasonality of food sales, this may also be an indication that we can expect 4-5% value growths to be the norm for the rest of 2009 as food inflation continues to slow.”
A third of supermarket sales were goods on promotion in the reporting period, up from 28% a year ago.
The level of promotions increased most in Tesco, where 36% of sales value was through offers.
Waitrose was the fastest-growing multiple, with sales up by 10.5%, followed by Asda on 8% and Morrisons on 7.8%.