Symbols and independents fared badly as UK grocery inflation hit 9.9 per cent in the four weeks to July 10, adding £454 to Britons' annual bills amid a worsening cost of living crisis, industry data showed on Tuesday.
Market researcher Kantar said the inflation rate was the second highest it has seen since it started tracking supermarket prices in this way in 2008.
"We're likely to surpass the previous high come August," warned Fraser McKevitt, Kantar's head of retail and consumer insight.
Kantar said sales on a value basis rose 0.1 per cent at market leader Tesco over the 12 weeks to July 10, but fell at Sainsbury's, Asda and Morrisons as shoppers switched to German-owned discounters Aldi and Lidl.
Lidl was Britain's fastest growing grocer over the 12 weeks with sales up 13.9 per cent, while Aldi's were up 11.3 per cent.
Both hit record market shares, with Lidl at 7.0 per cent and Aldi at 9.1 per cent - just 0.3 per cent below Morrisons, Britain's No. 4 grocer.
"Over 67 per cent of people in Britain shopped in either an Aldi or a Lidl in the past 12 weeks, with 1.4 million additional households visiting at least one of the discounters in the latest three months compared with last year," said McKevitt.
Symbols and independents have been the worst performers, with a 10.9 per cent decline in the same period.
The researcher said prices are rising fastest in markets such as dog food, butter and milk.
Food inflation could reach 15 per cent this summer and 20 per cent early next year according to some forecasts.
Kantar said as prices rise Britons are also increasingly turning to own-label products to drive down the cost of their weekly shop. Sales of supermarkets' own lines grew 4.1 per cent over the 12 weeks, while sales of branded items fell 2.4 per cent.
Kantar said its data also showed Britons preparing for the current heat wave, with sales of ice cream and suncare products soaring by 14 per cent and 66 per cent respectively over the past four weeks.
It said total UK supermarket sales rose 0.1 per cent over the 12-week period - the first time the market has registered growth since April 2021.
