Market researcher Kantar Worldpanel said Aldi's sales rose 19.8 percent in the 12 weeks to May 21 year-on-year, while Lidl's increased 18.3 percent, giving a joint record combined market share of 12 percent.

Grocery price inflation was recorded at 2.9 percent year-on-year, up from 2.6 percent in the previous period.

It said some higher prices such as for butter, fish and cola were partially offset by falling prices in other categories including cooking sauces and cooked poultry.

Kantar Worldpanel said 62 percent of the UK population shopped in an Aldi or Lidl during the 12-week period compared with 58 percent this time last year – an additional 1.1 million households.

“Consumers are starting to feel the pinch as prices continue to rise, with the average household spending an additional 27 pounds on groceries during the past 12 weeks," said Chris Hayward, consumer specialist at Kantar Worldpanel.

Overall sales in the market increased by 3.8 percent, the biggest rise since September 2013.

All 10 grocers saw a sales rise, boosted by the inflation.

Market leader Tesco's sales growth was 1.8 percent, Sainsbury's was 1.7 percent, Asda's was 0.9 percent and Morrisons' was 1.9 percent.

However, all the big four saw their market shares edge lower.

Separately on Wednesday two surveys showed British consumer confidence edged up to a four-month high in May but households remained downbeat about the economic outlook, with inflation since last year's Brexit vote feeding into higher prices in stores.

(Reporting by James Davey; Editing by Greg Mahlich)