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 had broadened their shopper basex
At the other end of the market, Waitrose performed strongly with 6.7% growth and an improved market share of 4.7%.
Lidl recently said it wants as many as 1500 stores in the UK, under plans to build on its rapid growth of recent years.