Through its media agency, Initiative, Tesco booked a full-colour campaign in all of Wednesday's popular and mid-market newspapers, taking all available colour ad slots in the first 20 pages of each title.
However, Asda booked a spoiler campaign to run in the first full-page colour ad slots available following the Tesco spots. Its ads claimed that Asda sells 3,457 products cheaper than Tesco.
One agency press director said the Tesco campaign, across The Sun, Daily Mirror, Daily Star, Daily Mail and Daily Express, would have cost in the region of £450,000. It would have cost Asda, through its media agency Carat, around £120,000 to run the spoiler ads, he added.
The source suggested that a client such as Tesco would usually have category exclusivity built into such a campaign to prevent knocking ads.
Initiative said it did not demand category exclusivity because the campaign carries a specific brand message from Tesco. A spokeswoman said: "We are incredibly happy with our campaign, the client is very happy with the campaign and the Asda campaign is not a spoiler."