Supermarket giant Tesco has been censured by the Advertising Standards Authority (ASA) for the second time in a year for making “ambiguous and misleading” claims.

The advertising watchdog investigated a press and TV ad, which ran last October, following complaints from rival Asda.

A press advert, which was based on Clubcard transactions on September 28, showed a stack of green Asda baskets and a taller stack of blue Tesco baskets with text saying “1,117,000 baskets cheaper”.

It added: “On Monday, when we compared prices with Asda, shopping was cheaper for more than a million Tesco customers. We compare every product our customers buy that we can match with an equivalent at Asda. This means we include more than half of everything our customers buy.”

The TV advert promoted special offers on port, biscuits and toilet paper. It also showed a stack of green Asda baskets and a taller blue stack of Tesco baskets. Text over the blue baskets said “1,050,000 cheaper” while text over the green baskets said “695,000 cheaper”. A voice-over said: “These are just three of hundreds of special offers in store each week, to help you spend less each week, and when we compared prices with Asda on Monday, shopping was cheaper for over 1 million Tesco customers …”

The advertising watchdog ruled that both ads were misleading because Tesco listed more than 31,000 lines on, but only matched around 12,000 of them with Asda. It added that the reference to baskets was also misleading because the retailer could not match all items in each basket.

The press ad breached rules on “truthfulness” and comparisons with identified competitors; while the TV ad broke rules on misleading advertising.  The ASA ruled that neither ad should be used again in their current form.

The ASA banned comparison ads from Tesco last July also following a challenge for Asda and a member of the public.  Asda has since introduced a promise to refund shoppers if they find a better offer at their nearest competitor. A website allows shoppers to check their receipt to see if eight or more products would have been cheaper elsewhere.