Half of households shopped at Aldi or Lidl over the past three months as the discounters captured more of Britain's grocery spending.
The shift in shopping habits was revealed by research firm Kantar Worldpanel, with Aldi now boasting a record 4% share of the market since growing its sales by 30% from a year earlier.
Lidl's share for the 12 weeks to December 8 was 3.1% thanks to year-on-year growth of 15.5%, Kantar said.
The budget chains have turned up the pressure on the big four supermarkets as households continue to struggle under financial pressure.
Tesco's market share fell to 29.9% from 30.6% a year earlier, while the strongest sales performance of the big four failed to prevent Sainsbury's from slipping to 16.8% from 17%.
Kantar Worldpanel director Chris Longbottom said Aldi and Lidl successfully broadened their shopper base, with half of all British households visiting one of them during the latest period.
"Aldi now boasts a record 4% of the grocery market, having increased its share for nearly every 12-week period since the end of 2010. Lidl retains its record share of 3.1% which it reached during the summer," he said.
Lidl recently said it wants as many as 1,500 stores in the UK, under plans to build on its rapid growth of recent years.
UK managing director Ronny Gottschlich described new Lidl customers as ''Maidstone Mums'', those who were once too embarrassed to be seen in Lidl shops.
"I think that people's perception in the past, and this is something that is definitely changing, is there must be something wrong with the quality of what those people at Lidl offer because they have such reasonable pricing in their stores," he said.