The British arm of German discount supermarket group Lidl saw its sales rise 2.6% in the four weeks ending December 26 year-on-year, as it benefited from shoppers switching from other grocers.
Lidl GB, owned by Germany's Schwarz group, said it achieved £21 million (€25.2 million) of switching gains from other food retailers.
It said its sales were up 21% on a two-year basis.
Marks & Spencer Outperforms
Elsewhere, Marks & Spencer was Britain's fastest growing food retailer in the key Christmas quarter, market researcher NielsenIQ said, providing further evidence that the company's latest turnaround programme is gaining traction.
NielsenIQ said M&S's grocery sales soared 9.4% in the 12 weeks to January 1 from the same period a year earlier, with growth accelerating from its November report.
In November, M&S said it had beaten forecasts for first-half profit and upgraded its earnings outlook for the second time in three months, sending its stock soaring on bets that one of Britain's most elusive turnarounds could finally materialise.
Its shares have now surged 84% over the last year.
Some analysts believe M&S, which also sells clothing and homeware, could upgrade its 2021-22 profit outlook again on Thursday when it publishes its own third-quarter trading update.
NielsenIQ's data showed market leader Tesco was the best performer of Britain's so-called Big Four grocers.
Increased Christmas Spend
The researcher said UK shoppers spent a total of £7.1 billion at supermarkets in the two weeks to December 25, up from £6.7 billion in 2020.
Sainsbury's will give an update on its Christmas trading on Wednesday, while Tesco will provide an update on Thursday.
The British arm of German discount supermarket group Aldi said on Monday its sales in December rose 0.4% compared with the previous year.