Three men who were arrested by police investigating the horse meat mis-labelling scandal have been released on bail, as officials continued to examine evidence from three more plants.
The Food Standards Agency (FSA) said it had passed on evidence from two premises in Tottenham and one in Hull to Europol - the European Union's law enforcement agency - after investigators, accompanied by police officers and local authority officials, removed meat samples for testing.
The move comes after Dafydd Raw-Rees, 64, the owner of Farmbox Meats near Aberystwyth, and a 42-year-old man, were arrested in Wales on Thursday on suspicion of offences under the Fraud Act. A 63-year-old man was also arrested on suspicion of the same offence at Peter Boddy Slaughterhouse in Todmorden, West Yorkshire.
The men have been released pending further inquiries and will return to answer bail in Aberystwyth at a later date, Dyfed Powys Police said.
The FSA has conceded it is unlikely the exact number of people in the UK who have unwittingly eaten horse meat will ever be known. Chief executive Catherine Brown said that testing was the right way to address the issue, and said the focus would be on areas of higher risk. But she admitted that the number of people who had unknowingly eaten horse meat was likely to be impossible to ascertain.
"I don't think that we ever will (know how many), because these tests are a snapshot, so even where we find things it is very hard to work out how long, what number of batches, so I think it is unlikely that we will ever know that. It is shocking," she said.
Her comments came as the head of a major UK supermarket chain insisted that the horse meat scandal was not "the tip of an iceberg". Justin King, chief executive of Sainsbury's said that supermarkets had not been slow to react to the scandal, but conceded there was a long way to go before the food industry could fully explain how the crisis has come about.
Meanwhile, almost a third of voters (31%) have stopped eating ready-meals as a result of the scandal, a poll suggested, and as many as one in 14 (7%) have stopped eating meat altogether.
The ComRes survey for the Sunday Mirror and the Independent on Sunday also found a majority in favour of a ban on all meat imports "until we can be sure of their origin" by 53% to 33%.
There was encouraging news for the Government as well: 44% said it had responded well to the crisis against 30% who disagreed. ComRes interviewed 2,002 adults online on February 13 and 14.