New year, new price cuts. And new ads. As the supermarkets battle to prove the real steal on pricing, Tesco has wheeled out Real Baskets, to challenge Asda's Dad's Army arrows.

Tesco's new campaign uses 220,000 'real' shops, from Clubcard records, to conclude Tesco would have been cheapest for 1.2 million of its shoppers, while Asda would have been cheaper for 645,000.

Based on Nielsen numbers this week, however, Tesco will need to have more success than with previous efforts. The swingometer, introduced in 2007, was attacked by Sainsbury's Justin King as "inaccurate, to say the least". And a Tesco basket comparison ad that ran in 2008 was rapped by the ASA.

The difficulty Tesco faces is one of perception. Credible price comparison should be based on a basket that represents what customers actually buy, but if the results are to be believed, independence can be more compelling. (Unlike rivals, The Grocer 33 meets both criteria, by the way.) Persistence helps here too. Asda has banged the same drum for a long time, while Tesco is just as likely to plug personal finance as basics.