Meat in Tesco burgers which was found to contain horse DNA did not come from an approved supplier, the supermarket said.
The meat also came from outside the UK or Ireland, contrary to Tesco policy.
The retailer has dropped its burger supplier, Silvercrest, following what it termed a "breach of trust".
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It has vowed to introduce a DNA testing system on meat to "ensure the quality" of food on its shelves in the wake of the scandal.
It said: "The evidence tells us that our supplier, Silvercrest, used meat in our products that did not come from a list of approved suppliers we gave them.
"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."