Lidl was found to be the cheapest for five months, including December, but Aldi nipped the top spot by being cheapest for six of the last 12 months, the annual study by consumer Which? found.
In January last year, the two rivals were tied with a basket of 19 items at both stores pricing at £18.45.
Cheapest supermarket of 2021
Aldi narrowly beat Lidl, the cheapest supermarket in 2020, to be crowned the cheapest supermarket last year.
However, Lidl was found to be the cheapest supermarket in December, at £23.29 for a basket of 22 groceries, just beating Aldi where the basket was priced at £23.64.
Meanwhile Waitrose was more than £9 pricier than Lidl, at £32.85, and was consistently the most expensive supermarket across the year.
A basket of everyday items at Waitrose cost from £6 to over £10 more per month than the cheapest alternative, Which? found.
How much have grocery prices risen?
Which? tracked hundreds of thousands of grocery prices across the UK’s eight big supermarkets, finding that they were charging up to 9% more in December than they did last January.
For a basket of 19 items, prices rose by an average of 3.4% over the last year.
Waitrose prices increased the most – by 9.2% – and Sainsbury’s the least, at 0.59%.
It was found that these items rose in price the most: Royal Gala apples (up 14%), free-range eggs (up 12%), brown onions (up 11%), skimmed milk (up 10%) and semi-skimmed milk (up 9%).
How was the study carried out?
Items on the shopping list were selected to ensure they were as comparable as possible across the retailers on factors such as their weight and quality.
The list combined branded items such as Kenco coffee, Oxo stock cubes and PG Tips tea bags with own-label products including onions and milk.
Which? also compared a larger trolley packed with 70 items not always available at Aldi and Lidl, such as Cathedral City cheddar cheese and Kenco coffee.
This found that Asda was the cheapest of the traditional supermarkets at £135.07 – £18.30 cheaper than the most expensive, Waitrose.
What’s been said?
Which? retail editor Ele Clark said: “Our findings show that while prices are going up, some supermarkets are passing their rising costs on to shoppers more than others.
“No one wants to overpay for basic groceries, especially when a cost-of-living crunch is putting extra pressure on household budgets.”
To help customers save on their weekly shop this year Ms Clark offered some advice.
She said: “As well as choosing a supermarket that is cheap overall, other ways to save include swapping from branded to own-brand products, sticking to a shopping list and resisting the temptation to pick up special offers you don’t need.”
After being revealed as the most expensive supermarket last year, a Waitrose spokesman responded to the survey's findings.
The spokesman said: “We’re working hard to deliver great value, offering ethically sourced, great-quality products at fair prices along with excellent service from our partners.”
A version of this article originally appeared on NationalWorld.com