The cost of a basket of staple goods has risen in Tesco, Dunnes Stores and Superquinn since the official axing of the order on March 20, a survey by independent consumer web site shoppingbill.com found.
Eggs, butter and tea are now more expensive, it said, and so too are other items, such as a pack of Denny's cooked ham, a 12-packet bag of Tayto crisps, a two-litre bottle of Coca-Cola, Squeez orange juice and a jar of Little Chip marmalade.
The findings are in stark contrast to the sharp fall in prices predicted by those who argued for the order's abolition. OFT chief executive John Fingleton, formerly head of the Irish Competition Authority, had forecast that the lifting of the ban would save consumers E500 a year on food bills.
None of the chains, which together account for more than 55% of the Irish market, would comment. Trade and enterprise minister Micheal Martin said it was too early to make an accurate assessment.