Tesco has been accused of making misleading claims in its adverts that stated 1.2m of its baskets were cheaper than at Asda.

The Advertising Standards Authority (ASA) said the adverts were not based on “like-for-like” products and the analysis was only based on 218,455 transactions.

The ASA said that the Tesco was not allowed to repeat the claims made in the adverts.

Another advert that claims Tesco is ‘Britain’s Biggest discounter’ have also been deemed as misleading and will not be allowed to appear in their current form.

A spokesman for Tesco said: “The ASA agreed with us that the term ‘Britain’s Biggest Discounter’ was open to a wide variety of interpretations and they acknowledged that Tesco could substantiate the claim in many different ways including by selling more cheap products than anybody else and giving the most amount of money back to consumers through discounts and promotions.

“The important thing for us is what our customers think and they have voted with their feet. Since we launched our discounter ranges more than 30% of our customers are now buying the products and according to independent industry figures fewer customers are turning to Aldi.”

Separately an investigation has been launched by Leeds City Council after a letter in support of a new Tesco store in the Yorkshire town was discovered to be a fake, according to The Telegraph.

Tesco said that it was “appalled” that someone had forged a letter. Hundreds of other letters relating to the application are now being checked.