The Food Standards Agency (FSA) says its investigation into the horsemeat beef burger scandal is focusing on European suppliers who sent their products to the companies that made the burgers for the supermarkets.
The FSA says their colleagues in Ireland found one sample that was positive for horse DNA in raw materials sent from Europe to the Silvercrest processing plant in Ireland.
The FSA is now looking to see if raw materials supplied to the Dalepak plant in Yorkshire from Europe are also contaminated - and whether the two plants have the same European suppliers.
The horsemeat scandal demonstrates how long and complicated the food chain we all depend on is. Regulating our food supply is expensive.
Some of the best, and worst, jokes and gags from Twitter users discussing the discovery of horse DNA in some supermarket beef burgers.
We've seen the jokes on Twitter but the discovery of horse and pig DNA in beefburgers poses a serious question; where did it come from?