Almost one in eight Brits did their single biggest December grocery shop at either Aldi or Lidl, new figures show.
Lidl was the fastest growing supermarket overall over the Christmas period with sales up by 18.5%, thanks in particular to an expanded premium range which contributed to customers increasing their average basket size by 7% to £17.20, according to Kantar Worldpanel.
Aldi followed with an increase in sales of 13.3%.
Waitrose, the Co-operative and Sainsbury's also grew ahead of the market in the 12 weeks to January 3 as sales across the grocery market fell 0.2% on last year because of continuing price deflation.
Sainsbury's was once again the best performer of the traditional supermarkets, with its premium Taste The Difference brand posting its biggest-ever Christmas sales, and straightforward price cuts rather than multi-buy deals helping to attract an additional 114,000 shoppers, leading to a 0.8% sales increase on last year.
Tesco sales fell by 2.7%, while its market share dropped to 28.3%, while Asda and Morrisons also saw their share declining to 16.2% and 11.0% respectively.
Kantar Worldpanel said Morrisons' share loss was expected as it continued to feel the effects of recent store closures, while the retailer had not repeated last year's Christmas Bonus loyalty cash promotion.
However the Bradford-based grocer today revealed a surprise rise in sales over the festive season, reporting a 0.2% rise in like-for-like sales excluding fuel in the nine weeks to January 3.
Waitrose benefited from shoppers trading up at Christmas, as usual, leading to a sales increase of 1.5% and its market share increasing to 5.2%.
The Co-operative also won market share at Christmas for the first time since it acquired Somerfield, seeing a sales growth of 1.4% to secure 6% of the market.
Fraser McKevitt, head of retail and consumer insight at Kantar Worldpanel, said: "Shoppers reaped the benefit of falling prices this Christmas, with groceries 1.8% cheaper than last year.
"The amount spent on a typical Christmas dinner fell even faster - down by 2.2% - mainly due to cheaper poultry and traditional vegetable trimmings.
"Wednesday December 23 was the single biggest shopping day of the year, but the anticipated uplift from an extra day in the week before Christmas didn't help the supermarkets overall. Consumers simply delayed their shopping trips later this year, rather than making any extra trips."
He added: "The discounters are continuing to establish themselves in the minds of British consumers - almost one in eight did their single biggest December shopping trip in Aldi or Lidl, on top of the 15.6 million households who visited at some point in the 12 weeks.
"That is an increase of nearly one million shoppers on last year, and their combined share is up from 8.3% last year to 9.7%."