Supermarket sales fell flat compared with last year's bumper summer, according to figures for the last three months.
Data from Kantar revealed all of the Big Four supermarkets - Asda, Morrisons, Sainsbury's and Tesco - saw a year-on-year dip in sales and smaller market share in the 12 weeks to August 11.
Fraser McKevitt, head of retail and consumer insight at Kantar, said: "The memory of last year still looms large for retailers and this summer's comparatively poor weather, combined with low levels of like-for-like price rises, have made growth hard to find for retailers.
"July's hottest day on record wasn't enough to shift the market into growth, but the grocers will have been encouraged by glimpses of better weather during the past four weeks which helped boost sales of summer staples like hayfever remedies, suncare and burgers by 17%, 8% and 5% respectively."
Sainsbury's showed the smallest dip in the cohort of 0.6%, driven by higher levels of promotion which helped boost sales of branded goods.
Meanwhile, Ocado was the fastest-growing UK grocer, notching up a 12.6% rise. But the online supermarket only accounts for 1.4% of the market.
Lidl's growth was the next fastest, at 7.7%, to give the discounter a record total market share of 5.9%.
Rival Aldi posted a 6.2% increase in sales, supported by an 11% rise in bakery products and a 13% increase in biscuits.
Nearly half of all households in the UK shopped in an Aldi during the last 12 weeks.
