Lidl beat Aldi to the title of cheapest supermarket in March by just 3p, according to the latest monthly analysis from Which?.
We compared prices for a trolley of 20 items. On average, shoppers would have paid £22.48 at Lidl, which beat fellow discounter Aldi by just 3p. Meanwhile, the most expensive supermarket was more than £7 pricier than Lidl for an equivalent trolley of groceries.
Here, we reveal the month's most expensive as well as cheapest supermarkets.
Every day throughout March we checked the prices of 20 items, including own-brand products such as apples, eggs and tomatoes and branded goods such as Hovis wholemeal bread, to see how UK supermarkets compared. Here's how much our trolley cost on average:
Lidl came out cheapest overall at just £22.48. Asda was the cheapest 'big four' supermarket, with our trolley costing £24.76.
At the other end of the scale, upmarket Waitrose was over £7 more expensive than Lidl, at £29.77 - that's 32% more.
Groceries with some of the biggest price differences included own-label large free-range eggs, which had a difference of £1.15 between Lidl and Waitrose, and own-label rocket, which had a difference of 86p.
Of course, price is just one factor when you're deciding which supermarket to shop at. We also survey shoppers about quality, customer service, store experience, online deliveries and a range of other factors to reveal the each year.
We also compared a shopping trolley packed with 85 items (the original 20, plus 65 more). This included a greater selection of branded items, such as Branston baked beans and Kleenex tissues, that aren't always available in the discounter supermarkets - so for our bigger trolley we haven't been able to include Aldi or Lidl.
Asda, at £160.42, was by far the cheapest of the traditional supermarkets. It was a huge £21.22 cheaper than the most expensive supermarket, Waitrose. Grocery prices at Sainsbury's and Morrisons were similar, with just £1.50 separating them.
We can't compare exactly the same items each month because products aren't always available at every retailer, but Asda has been the cheapest mainstream (non-discounter) supermarket for more than a year now, having claimed the title every month since January 2020. You can shop with it online at .
We tracked the prices of 20 items at the UK's six biggest supermarkets throughout March. For our larger trolley analysis we added a further 65 items for all supermarkets apart from Aldi and Lidl, where the products were unavailable.
Using an independent price comparison website, we calculated the average price (including special offers but not multibuys) for each item throughout the month. We added those individual averages together to give an overall price for the trolley at each shop for the month.
Our shopping list combined branded items, such as Kenco Millicano coffee, Oxo stock cubes and Twinings English breakfast tea, with own-label products including onions, tomatoes and milk. Of course, own-brand items aren't exactly the same at different supermarkets, but we've used experts to ensure that the products are as comparable as possible based on a range of factors, including weight, quality and other industry data.