LONDON (AP) _ Prime Minister John Major said Tuesday that his government would investigate reports that meat inspectors warned of poor sanitation in slaughterhouses well before an outbreak of food poisoning that killed 20 people.

The government, which must face national elections by May, has been put on the defensive by reports that the Association of Meat Inspectors, a trade body, wrote to government ministers in the past nine months to warn that hygiene standards in slaughterhouses left ``much to be desired.''

The revelations raise new questions about the quality of British meat, the reputation of which was seriously tarnished by last year's ``mad cow'' outbreak.

Twenty people, mostly elderly, have died in an outbreak of food poisoning in Scotland that health officials said was caused by E. coli bacteria from contaminated meat.

On Thursday, Agriculture Minister Douglas Hogg denied in Parliament that he had suppressed the results of an investigation into unhealthy conditions in slaughterhouses. The 1995 report by the government's Meat Hygiene Service warned that E. coli was winding up in slaughterhouses because of unhygienic practices.

Tony Blair, leader of the main opposition Labor Party, said Tuesday that the correspondence revealed the situation in slaughterhouses was ``getting worse, not better.''

Blair urged Major to set up an independent food safety agency.

Challenged by Blair to pursue the reports that AMI inspectors alerted authorities about hygiene problems in the slaughterhouses, Major replied, ``I will most certainly do so. I entirely share your concern and the AMI's (concern) to ensure the highest standards of hygiene in slaughterhouses.''

The Meat Hygiene Service, a part of the Ministry of Agriculture, carries out slaughterhouse inspections.

In a statement, Food Minister Angela Browning said the Meat Hygiene Service has dismissed three staff and formally disciplined 41 others for failing to enforce safety rules properly. Extra staff have been loaned to the service, including some 250 inspectors.

A year ago, the British government conceded that mad cow disease was the likely cause of a new strain of the fatal brain-wasting Creutzfeldt-Jakob disease in humans. Mad cow disease, called Bovine Spongiform Encephalopathy or BSE, has been linked to the practice of mixing ground-up sheep into cattle feed.