How did horsemeat get into the food chain?

One of the factories involved, Dalepak Hambleton, says it is likely to have come from a minor ingredient in the burgers, as all but one of the burgers had very low levels of the DNA. The investigations will focus on suppliers to the factories. The huge amount of DNA in one product does raise questions about whether more major ingredients were contaminated.

A statement from Silvercrest said: "Silvercrest has never purchased or traded in equine product and has launched a full-scale investigation into two continental European third-party suppliers who are the suspected source of the product in question."

As well as the burgers, the FSAI analysis found small traces of horse DNA in batches of raw ingredients, including some imported from the Netherlands and Spain. However, these weren't ingredients that had been used in the tested burgers.

Raymond Ellard, the FSAI's director of consumer protection, told RTE radio this morning that the low level of the DNA did not seem to be "evidence of some widespread subterfuge where someone is trying to substitute horse meat for beef".

How does pig meat get into beefburgers?

Meat from different animals is processed in the plants identified by the Food Safety Authority of Ireland (FSAI), and it is possible that traces contaminated the areas that were processing the burgers.

Are there any health risks?

There shouldn't be health risks simply from eating horsemeat – it is widely consumed in other countries. But the fact its origin is unknown could ring alarm bells. The FSAI says it doesn't consider the presence of horse or pig DNA in the burgers to be a food safety risk, but it is keen to find out how it got there.

Does it taste any different?

Apparently not. The problem was detected through routine testing rather than after consumer complaints, suggesting many of those who had bought the products did not notice anything unusual.

Is it illegal?

It isn't illegal to sell horsemeat to be eaten in the UK. However, there are laws on how food is described on packaging, and the FSAI tests were part of its work to make sure firms were complying with these. It is not yet talking about taking action against the manufacturers, and says retailers have withdrawn the products voluntarily. However, if the investigations suggest rules have been broken there could be later legal repercussions.

How can you guarantee the content of your burger?

You could buy one of the ones on the list that tested negative: Iceland Beef Burgers, Supervalue Daily Basics Beef Burgers and Simply M&S British Beef Burgers all tested negative for traces of horse and pig DNA in the FSAI's tests. A good butcher who knows the source of the meat on sale should also help reassure you.