Sales volumes at the UK’s leading supermarkets have fallen year-on-year for the first time since early December 2014, according to latest Nielsen data.

Declines in soft drinks, frozen foods and general merchandise were behind the -0.3% fall in sales volumes during the four weeks ending 15 August 2015.

The last year-on-year decrease was the four weeks ending 6 December 2014 (-0.4%), which preceded eight consecutive reported rises.

“The disappointing growth figures reflect the continuing unpredictable summer weather as well as the underlying deflation in retail prices,” said Nielsen’s UK head of retailer and business insight Mike Watkins.

“The week ending 25 July suffered from particularly poor weather with the value of sales down -3.6% against the same period last year, which was notably warmer and included the start of the Commonwealth Games.”

All of the big four supermarkets lost market share during the 12 weeks ending 15 August, with Tesco’s share down to 27.9% from 28.4% a year earlier. Asda had the largest decline in year-on-year sales (-3.4%), its sixth consecutive fall.

Discounters Aldi (22.6%) and Lidl (14.8%) continued to have the largest rise in year-on-year sales, and now together account for 10.4% of all UK supermarket sales.