Mainstream supermarkets such as Tesco have made price-matching the German discounters Aldi and Lidl a core part of their marketing, in an attempt to battle the rapid rise of the low-price retailers.
Tesco first said it would price-match Aldi in 2020 during the early months of the pandemic. It currently does so across 700 lines.
Tesco insisted that just because a product contains a higher proportion of one ingredient, it does not necessarily mean the overall quality is higher.
A range of factors including the quality of individual ingredients and how the product is produced should also be considered, it argued.
Not all of the products examined by BBC Panorama were found to contain less of the main ingredient.
In 12 cases, Tesco’s products contained more than Aldi’s, such as its Hearty Food Co. fish fingers, which contain 64pc Alaskan pollock compared with 58pc in Aldi’s Everyday Essentials version.
Tesco’s Eastmans coleslaw was also found to contain 57pc cabbage compared with 47pc in Aldi’s The Deli coleslaw.
Earlier this month Aldi announced plans to spend £800m on opening new stores across the country as bosses seek to narrow the gap between it and the third-largest supermarket by market share, Asda.
Giles Hurley, Aldi’s UK boss, at the time criticised efforts by traditional supermarkets to match it on price, saying: “I’m delighted that full-price, more expensive supermarkets have recognised us as the benchmark.
“These revolving price-matching schemes in full price supermarkets are a game of chance for customers. You know, they aren’t consistent. They do change. And our customers tell us they want certainty.”
Aldi’s sales surged by 15pc last year to a record £17.9bn, although its growth has slowed compared with rival discounter Lidl recently.
A Tesco spokesman said: “Since we launched our Aldi price match four years ago it has proved very popular with customers.
“We constantly review the quality of our products, and we have clear processes in place to ensure that the hundreds of products that are included are comparable with those sold at Aldi.”
Aldi was approached for comment.