Supermarket sales continued to edge upwards this month, increasing by 0.3 per cent for the three months ending 11 September.
The growth was against a backdrop of price deflation of 1.1 per cent.
Fraser McKevitt, head of retail and consumer insight at Kantar Worldpanel, said: “While overall sales growth has been slow, consumers have been keen to celebrate Britain’s Olympic and Paralympic golden summer, boosting alcohol sales by 8.5 per cent in the past four weeks.
"Sparkling wines including Prosecco and Champagne led the way with growth of 36 per cent as promotional events across a number of retailers successfully tapped into the nation’s celebratory mood."
Tesco's sales fell by 0.2 per cent year-on-year, which McKevitt said was its best performance since March 2014.
"This period, its "extra" and larger stores delivered a positive contribution to performance, though market share fell back by 0.1 percentage points and Tesco now accounts for 28.1 per cent of the overall grocery market,” McKevitt said.
Waitrose bagged a record market share of 5.3 per cent - but its proportion of promotional sales was higher than some of the 'big four' retailers.
For the 12 weeks ending 14 August, Kantar found the grocery market grew at 0.3 per cent due to the sunny summer weather, which was the fastest growth in the grocery market since March.
Kantar has been watching out for any food price inflation associated with the Brexit vote, but said that grocery prices had actually decreased.