The consumer group tracked thousands of branded grocery prices across six major supermarkets throughout 2019 to find out how much each shop was charging.
Which? experts compiled a list of 53 common grocery items, from Andrex toilet tissue to Weetabix breakfast cereal, and found that the goods cost just £107.01 a month at Sainsbury's on average across the year.
In stark contrast, the exact same items would have set you back £117.81 a month at Waitrose – 10 per cent more and potentially costing shoppers an annual total of £129.60 more than if they had done the equivalent shopping at Sainsbury's.
Asda came in as the second cheapest supermarket, with an average monthly cost of £107.65 for the items on Which?'s shopping list. Morrisons followed closely behind in third place, charging £109.13.
Which? collected the data by monitoring online pricing, which means that only shops selling all of the branded items online - Asda, Morrisons, Ocado, Sainsbury's, Tesco and Waitrose - have been included in the ranking.
The consumer group ran a similar price comparison last year, and found that Morrisons was the cheapest supermarket of 2018, followed by Asda and then Sainsbury’s.
The likes of Aldi and Lidl continue to grow their market share in the UK, but neither offer an online shopping platform for the branded items included in the Which? study.
Natalie Hitchins, Which? Head of Home Products and Services, said:
"Your weekly supermarket shop can have a significant impact on your wallet, and the start of a new year is a good time to look at your household spending to see if there are areas where you can save money.
"Our analysis shows how important it can be to shop around to ensure you get the best price for your groceries."
|Supermarket||Average cost of trolley (53 branded items)|
The Which? shopping trolley for this analysis included bread, crisps, butter, cheese cleaning products, pet food, soft drinks and other everyday items. Specifics products included:
- Alpen Original Muesli (750g)
- Ben & Jerry’s Cookie Dough Ice Cream (500ml)
- Dolmio Bolognese Sauce – Original (500g)
- Innocent Pure Fruit Smoothie Mangoes & Passion Fruits (750ml)
- Knorr Stock Cubes Vegetable (8x10g)
- Mr Kipling Cherry Bakewells (6)
- Sure Men MotionSense 48hr Anti-Perspirant – Active Dry (250ml)