Findus says it is "sorry that we have let people down", in a fresh statement.
However, the horsemeat lasagne had been supplied to Findus by the French food company, Comigel.
Findus said the product was manufactured by a third party supplier and not by Findus.
The furor over the Findus lasagna prompted humor as well as outrage on Twitter.
Findus has been ordered to test the lasagna withdrawn from the shelves for the drug's presence.
Findus UK became caught up in the row this week after horsemeat was found in its lasagne.
Meanwhile, Bracknell Bees are planning to leave the Superleague and join the Findus British National League next season.
The supermarket giant Tesco, frozen food firm Findus and budget chain Aldi received mince containing horsemeat from Comigel.
Findus said it had been told that its products were being made with French beef, not Romanian horsemeat.
CNN: Meat industry under scrutiny as horsemeat scandal spreads
That letter had made Findus "aware of a possible August 2012 date" for the contamination, the company said.
CNN: Meat industry under scrutiny as horsemeat scandal spreads
Findus has been ordered to test the lasagna withdrawn from shelves in the United Kingdom for the drug's presence.
CNN: Meat industry under scrutiny as horsemeat scandal spreads
Findus said on Friday that it had tested all its other beef products and found no evidence of contamination.
BBC: Jersey health plans law change to challenge mis-labelling
It said beef lasagne was the only product affected and it was sourced externally rather than manufactured by Findus.
It follows the discovery that Findus lasagne contained up to 100% horse meat.
BBC: Jersey health plans law change to challenge mis-labelling
The Food Safety Authority of Ireland said Friday that the affected Findus lasagna had also been sold in Ireland.
Comigel alerted Findus and Aldi that their products "do not conform to specification".
But Findus is only one of several companies that receives products from Comigel.
CNN: Horsemeat found in beef products, search on for 'villain'
Findus France has said it will take action in the French courts, believing itself to be the victim of fraud.
Findus Nordic, which oversees Findus throughout the Nordic region, said it has begun legal action against Comigel and its subsuppliers.
CNN: Battle over blame after horse meat found in beef products
Findus said a letter from Comigel dated February 2 informed Findus that the contamination may date back to August 2012.
CNN: Battle over blame after horsemeat found in beef products
Six French supermarket chains - Carrefour, Monoprix, Auchan, Casino, Cora, and Picard - have also withdrawn ready-meals from Findus and Comigel.
Samples of the affected Findus lasagna also contained between 60 and 100% horsemeat, according to UK and Irish food safety inspectors.
CNN: Meat industry under scrutiny as horsemeat scandal spreads
Some Findus frozen beef in lasagne, made by a French food processing company, was found to be up to 100% horsemeat.
They advised them to remove Findus Beef Lasagne and Aldi's Today's Special Frozen Beef Lasagne and Today's Special Frozen Spaghetti Bolognese.
Ed Bedington, editor of Meat Trades Journal, says the Findus horse meat case has brought into question the security of supply chains.
The French arm of Swedish frozen food firm Findus said it would file a legal complaint Monday against the unnamed Romanian business.
CNN: Meat industry under scrutiny as horsemeat scandal spreads
The meat was then sold under the Sweden-based brand, Findus, which has said it has been misled by its Romanian meat supplier.
The Findus products were prepared by French food manufacturer Comigel using meat provided by Spanghero, a meat-processing company also based in France.
The products were pulled Monday after French supplier Comigel raised concerns about the type of meat that was used, Findus Sweden said.
CNN: Horsemeat found in beef products, search on for 'villain'
Comigel produced the now infamous lasagna for Swedish frozen food brand Findus.
FORBES: The Romanian Horse Cart Ban That's (Probably) Behind Europe's Horse Meat Scandal
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