The UK’s advertising watchdog has ruled that adverts run by retailer Asda are “misleading and untruthful” and must not appear again in their current form.

The ads for Asda’s Price Guarantee, which aired from April last year, promised to refund customers the difference during their next shop if they found groceries cheaper at other major supermarkets. However, Morrisons and Tesco filed complaints with The Advertising Standards Authority (ASA) claiming that there were “significant exclusions” from the price comparison.

Morrisons said that the information captured by mysupermarket.co.uk and used as the basis of the price comparison “could not guarantee an accurate reflection of the price of goods sold in Morrisons”.

Nine complaints were made by rivals in total – with the ASA upholding four.

The watchdog said that Asda did not make it clear enough that the price guarantee did not apply to non-grocery products, such as books and football-related items that appeared in the adverts.

The ASA ruled that the adverts should not run again in this form, and that the company should make it clear that non-grocery items were included in the offer.

In a statement in response to the ASA ruling, Asda said: “It is worth remembering before we launched the original Asda Price Guarantee (APG) in April last year the ASA and Clearcast signed off the fact that the APG covered ‘comparable grocery shopping’ – nearly 15,000 different grocery items.

“ASA was happy then with methodology and exclusion criteria and still is based on this latest ruling. Fresh items are included in the APG by independent price checker mysupermarket.co.uk on the basis there they are comparable by size, weight and composition, and stocked by Tesco, Morrisons, Sainsburys and Waitrose. There are more than 2,900 different fresh products to choose from – and the exceptions highlighted by Morrisons were shown to be just that, exceptions.”

Asda failed to return requests for further comment.