The supermarket price war is set to intensify after a study found Lidl was almost a third cheaper than the major chains.
The German low-cost business was included in The Grocer magazine's weekly price survey for the first time, which found that it sold a basket of common groceries for 29% cheaper than Tesco.
Lidl, which has 36 stores in Northern Ireland and plans to open another in Belfast's High Street, also scored 78 out of 100 for service at its High Wycombe store, just one point behind Tesco Extra in Streatham, South London.
It came level with Waitrose and beat Asda, Morrisons and Sainsbury's.
A weekly shop at Lidl cost £49.23, compared with £57.83 at Morrisons, £59.95 at Asda, £63.73 at Tesco, £64.50 at Sainsbury's and £71.84 at Waitrose.
Only three Lidl products could be found cheaper elsewhere – cauliflower at Asda and Chicago Town pizza and Laughing Cow cheese at Morrisons.
Both Lidl and fellow German discounter Aldi made record sales as price competition in the sector weighed heaviest on the country's big four players, according to figures released last month.