LONDON - The British government was last night embroiled in a fresh row over food safety after new evidence that ministers and their advisers were warned over several months about hygiene standards in slaughter houses. The Prime Minister, Mr Major, agreed to look into evidence that the Association of Meat Inspectors issued several warnings about the "potential time bomb" of contaminated meat. But the Food Minister, Ms Angela Browning last night stressed continuing efforts to improve standards, saying she hoped in future to be able to publish "league tables" of individual abattoir conditions.