Meat in Tesco burgers which was found to contain horse DNA did not come from a list of approved suppliers, the supermarket has said.
The meat also came from outside the UK or Ireland, which was contrary to company policy. The supermarket has dropped its frozen burger supplier, Silvercrest, following what it termed a "breach of trust".
It has vowed to introduce a DNA testing system on meat products to "ensure the quality" of the food on its shelves in the wake of the scandal.
It said: "The evidence tells us that our frozen burger supplier, Silvercrest, used meat in our products that did not come from the list of approved suppliers we gave them. Nor was the meat from the UK or Ireland, despite our instruction that only beef from the UK and Ireland should be used in our frozen beefburgers.
"Consequently we have decided not to take products from that supplier in future. We took that decision with regret but the breach of trust is simply too great."
Tesco was forced to issue a public apology earlier this month after tests in Ireland discovered traces of horse meat in three frozen beefburger lines.
The findings sparked a national outcry and 10 million burgers were taken off shelves as a result of the scandal. The supermarket launched an investigation into how the meat ended up in stores in the UK and Ireland on January 16.
It has promised to set a "new standard" with the introduction of a testing system designed to detect "any deviation from our high standards".
It issued a statement saying: "Ultimately Tesco is responsible for the food we sell, so it is not enough just to stop using the supplier.... To underpin the strong measures already in place, we will now introduce a comprehensive system of DNA testing across our meat products.
"This will identify any deviation from our high standards. These checks will set a new standard."
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