Aldi was the cheapest supermarket in June, according to the latest monthly analysis from Which?.
We compared prices for a basket of 18 items. On average, shoppers would have paid £21.61 at Aldi, which beat fellow discounter Lidl by just 20p. Meanwhile, the most expensive supermarket was almost £7 pricier than Aldi for an equivalent trolley of groceries.
Here, we reveal the month's most expensive as well as cheapest supermarkets.
Every day throughout June we checked the prices of 18 items, including own-brand products such as apples and eggs as well as branded goods such as Hovis wholemeal bread, to see how the UK's biggest supermarket chains compared. Here's how much our trolley cost on average:
At the other end of the scale, Waitrose was almost £7 more expensive than Aldi, at £28.59 - that's 32% more.
Groceries with some of the biggest price differences included own-label large free-range eggs, which had a difference of £1.06 between Aldi and Waitrose, and own-label chicken drumsticks, which had a difference of 85p.
Of course, price is just one factor when you're deciding which supermarket to shop at. We also survey shoppers on their experiences of supermarkets' product 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 76 items (the original 18 plus 58 more). This included a greater selection of branded items, such as Branston baked beans and Colgate toothpaste, 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 £141.02, was by far the cheapest of the traditional supermarkets. It was a huge £20.77 cheaper than the most expensive supermarket, Waitrose.
Grocery prices at Morrisons and Tesco were similar, with just £1 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.
We tracked the prices of 18 items at the UK's six biggest supermarkets throughout June. For our larger trolley analysis we added a further 58 items for all supermarkets apart from Aldi and Lidl, where the products were unavailable.
Using an independent price comparison website, we checked the price of each item every day throughout the month at all available supermarkets. We then calculated an average price for each item at each supermarket, and added the individual item prices up to generate an average trolley price for each store.
We included special offer prices but not multibuys to keep it as fair as possible.
Our shopping list combined branded items such as Kenco coffee, Oxo stock cubes and Twinings English breakfast tea with own-label products including onions 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.