The veterinary painkilling drug phenylbutazone - or bute - has been found in Asda Smart Price Corned Beef, the Food Standards Agency said.
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Several of victims had life-threatening injuries, police said.
The helicopter, which the royal was not in at the time, avoided a potentially deadly mid-air crash.
The shots on a bus sparked a major security scare as weekend tourists in some of the world's most famous casinos were told to bunker down.