Which? priced up 22 specific items from each of the supermarkets to make the comparison.
A basket of 22 branded and unbranded items would set shoppers back £24.03 at Aldi.
Just behind Aldi, Lidl’s shopping came to a total of £24.40 which was just 37p more expensive.
Waitrose was named the most expensive supermarket with their products costing £9 more than Aldi.
The basket from the supermarket giant came to a total of £33.06.
By comparison, Asda’s shopping list come to £26.19 and Sainsbury’s was priced at £27.95.
Shoppers at Morrison and Tesco would pay out the same price of £28.31.
Ocado was the second most pricey supermarket at £29.84, just behind Waitrose.
Aldi were delighted to be offering the best prices to shoppers in the UK.
Aldi managing director of buying Julie Ashfield said: “We’re committed to providing our customers the best prices possible, and we’re immensely proud that we have taken the top spot.
“Being named the UK’s cheapest supermarket in September marks our tenth win and we’re dedicated to continuing to make life a little easier for our customers.”
To collate the data for September, the Which? shopping list included unbranded products such as mixed peppers and semi-skimmed milk.
It also included staple branded items such as Andrex toilet paper, Colgate toothpaste and McVitie’s digestive biscuits.
Aldi had the top title in July earlier this year while Lidl was in the number one spot in August.