Aldi and Lidl claim the food and drink sold in their stores is cheaper but as good as that sold in Marks & Spencer and Waitrose.

In their submissions to the Competition Commis­sion's groceries inquiry, the hard discounters insisted it was simply the image of rival stores, including the big four, that created the perception that their offers were of a higher quality.

"In quality terms, there is no difference if individual products are compared on a direct basis," said Lidl.

"Customers' quality perception has got a lot to do with the perceived image of the respective retailer. Many of Lidl's and Aldi's products are of the same quality as Marks & Spencer's and Waitrose's but customer perception still widely disacknowledges this matter, although a look at the ingredients lists on the packaging would easily provide enlightenment."

Aldi compiled a table for its submission in which it categorised all major grocery chains and compared them to its own business.

The big four, Waitrose, M&S and Booths all offered bigger ranges than Aldi stores, it conceded, but also charged "higher prices for like-for-like quality".

It claimed other rivals - including Lidl - offered "poorer value for money" and a "poorer store environment".