Lidl was the cheapest supermarket in February, according to the latest monthly analysis from Which?.
We compared prices for a basket of 23 items every day last month and found that, on average, shoppers would have paid £24.21 at Lidl.
It beat rival discounter Aldi by just 62p.
Meanwhile, the most expensive supermarket was £9.50 pricier than Lidl for an equivalent basket of groceries. Here, we reveal the month's cheapest and most expensive supermarkets.
Every day throughout February we checked the prices of 23 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 basket cost on average:
At the other end of the scale, Waitrose was £9.50 pricier than Lidl, at £33.71 - that's 39% more. Groceries with some of the biggest price differences included PG Tips tea bags, which had a difference of £1.52 between Lidl and Waitrose, and own-label seedless grapes, which had a difference of £1.41.
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 trolley packed with 66 items (the original 23 plus 43 more). This included a greater selection of branded items, including Twinings tea bags, 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 £128.19, was the cheapest of the traditional supermarkets. It was £16.26 cheaper than the most expensive supermarket, Ocado.
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 26 months now, having claimed the title every month since January 2020.
We check the prices of hundreds of grocery items at eight major supermarkets every day throughout the year, using an independent price comparison website.
For our 'cheapest supermarket of the month' analysis, we work out the average price for each item at each supermarket across the month, and add the averages up to get an average trolley price for each store. We include special offer prices but not multibuys, to keep it as fair as possible.
Our shopping list combines 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 and quality.
Concerns about rising grocery prices continue to dominate the industry, with grocery price inflation at 4.3% in February, according to the latest figures from analysts Kantar.
Apart from the start of the pandemic, when grocers axed promotions to maintain availability, this is the fastest rate of inflation recorded since September 2013. On top of this, supply chain pressures and the potential impact of the conflict in Ukraine (which has seen surging prices for oil, fertiliser, wheat and corn) are set to continue pushing up prices.
Prices are rising fastest in markets such as savoury snacks, fresh beef and cat food, while falling in bacon, beer and lager, and spirits.
Kantar said households spent on average £26.07 less at supermarkets in February than the same time the previous year. Own-label sales did better than brands for the first time in three months too. But the drop in monthly spending isn't all down to savvy budgeting - more people are now eating on the go and enjoying meals out with friends and family. That means they are buying less food and drink to have at home.
The pressure on prices has also created a new twist in the price-matching war between Aldi and Tesco. It has emerged Aldi has actually raised some prices first - with Tesco following suit. Experts think it's a sign of Tesco's determination not to ease the pressure off Aldi despite rising inflation.