Aldi has been named the UK’s cheapest supermarket in March, coming out £20 cheaper than Waitrose but just 25p less expensive than Lidl.
A basket of 41 grocery items at Aldi cost £72.54 on average across the month, compared with £92.55 at Waitrose and £72.79 at Lidl, Which? Found.
Sainsbury’s was the next cheapest, costing £9.25 more.
Waitrose was £41.83 more expensive than Asda.
However, it said many of the major supermarkets had not done enough to support their customers during the cost of living crisis.
The watchdog said retailers should be helping customers by making sure affordable basic ranges were available in all branches, including smaller convenience stores, as well as improving unit pricing on all products to allow customers to easily work out the best value.
Which? Retail editor Ele Clark said: “We know people are suffering through the worst cost-of-living crisis in decades and the price of food and drink has skyrocketed no matter where you shop.
“However, our monthly supermarket analysis shows you could save £20 on a basket of everyday groceries at the cheapest supermarket compared to the priciest one.
“Supermarkets aren’t currently doing enough to help customers. Which? believes the big retailers have a responsibility to ensure everyone has easy access to basic, affordable food ranges at a store near them, and to provide transparent pricing so people can easily work out which products offer the best value.”
Last month, the Office for National Statistics reported that UK inflation shot up unexpectedly to 10.4% in February as vegetable shortages pushed food prices to their highest rate in more than 45 years.