Labour MP Tom Watson has published an extract of a letter which suggests Findus knew their product was mis-labelled as early as last Saturday.
He says the letter was passed to him by a retailer which withdrew the affected lasagnes after receiving the correspondence from Findus on Monday.
It suggests that suppliers informed Findus about the "non-conform" on Saturday and that the incorrect labelling could date back to 1st August 2012.
Investigations have led one of our suppliers based in France to inform us in writing on 2nd February 2013 that the raw materials delivered since 1st August 2012 are likely to be non-conform and consequently the labelling on finished products is incorrect.
The supplier has asked us to withdraw the raw material batches.
Findus said the affected lasagnes were withdrawn from shops on Monday before DNA test results came back on Wednesday.
A leading food scientist says the rule change that sparked the horsemeat beef scandal affected lamb products too, and they should be tested.
Retailers and the Food Standards Agency held an emergency meeting today to decide how to proceed with the horsemeat scandal.
The government has called an emergency meeting with retailers and the Food Standards Agency to discuss the horsemeat scandal.