Market researcher Kantar said all of Britain's big four supermarket groups - market leader Tesco, Sainsbury's, Asda and Morrisons - recorded sales declines over the period and lost market share to the German-owned discounters Aldi and Lidl which are aggressively opening new stores.
Kantar said total British grocery sales rose 0.5% year-on-year in the 12 weeks to Dec. 1, having increased 1% in its November data set.
"We’re yet to see consumers ramp up their spending in the run up to Christmas and, as anticipated, Black Friday only brought a limited boost for the grocers," said Fraser McKevitt, head of retail and consumer insight at Kantar.
“With the general election now only days away, people are waiting to fill their cupboards for the festive break," he said, noting, for example, that sales of Christmas puddings and seasonal biscuits are down 16% and 12% in the past four weeks, compared with this time last year.
Kantar said sales at Tesco fell 0.8% over the period, while Sainsbury's, Asda, and Morrisons saw sales declines of 1.1%, 1.9% and 2.9% respectively.
In contrast Aldi's sales were up 6.2% and Lidl's rose 9.3%, giving a combined market share of 14.1%.
“While the big four all lost share in the past 12 weeks, 98% of the British public still visited at least one of their stores during the past three months," said McKevitt.
"Based on previous years, we expect them to increase their proportion of sales in the coming weeks as shoppers turn to familiar favourites and the traditional retailers in December.”
Kantar said it was too early to say if Tesco's new "Clubcard Plus" loyalty subscription scheme, launched last month, has had an impact on sales.
Shares in Tesco were down 0.6% at 0932 GMT, while Sainsbury's was down 0.9% and Morrisons was down 2.9%.
Kantar said grocery inflation was 0.8% for the 12-week period. It said prices are rising fastest in markets such as fresh sausages, dog food and frozen fish, while falling in fresh poultry, instant coffee and butter.
(Reporting by James Davey, Editing by Paul Sandle and Jane Merriman)