UK retailers have rejected government criticism they "remained silent" over the horsemeat crisis - as they begin to release test results on beef products.
In a public letter, 11 firms, including Tesco and Asda, said they shared shoppers' "anger and outrage".
Many retailers say results so far show no sign of horsemeat, but pubs owner Whitbread and school supplier Compass Group found horse DNA in some products.
Number 10 said it was pleased retailers had finally spoken out in public.
A Downing Street source said: "Consumer confidence is one of the things that has been missing and that needs the retailers to explain themselves, and what they have been doing."
Earlier, Downing Street said big retailers selling affected products had a responsibility to answer key questions on the scandal.
Sources said it was not "acceptable for retailers to remain silent while customers have been misled about the content of the food they have been buying".
Meanwhile, the results of up to one third of tests on the presence of horsemeat in processed meals ordered by the Food Standards Agency (FSA) are being released.
Iceland said that all of its own brand beef products have been found to be free from horsemeat.
The Co-Operative Group said 59 of its 102 own-brand minced beef products have been tested so far, with all found to be clear of horsemeat. And Morrisons says 68 test results on its products have not found horsemeat, with more results still to come.
Tesco says tests on 149 of its products are clear, and Sainsbury's say their tests show no horse adulteration.
But Whitbread, which supplies thousands of pubs and owns Premier Inn, Beefeater Grill and Brewers Fayre, has confirmed two of its products have been found to contain horsemeat.
And Compass Group, one of the biggest school food providers in the UK, says its tests have found between 5% and 30% horse DNA in burgers it sold in Ireland and Northern Ireland.
It says the burgers were supplied by Rangeland Foods in County Monaghan, which previously withdrew more than 9,000 burgers made for the UK market after some were found to contain horsemeat.
A spokesman for Compass said the affected burgers had been supplied to a small number of sites on both sides of the Irish border, including two colleges which the firm would not name.
In other developments:
- Cottage pie delivered to 47 schools in Lancashire has tested positive for horse DNA. The product has now been withdrawn from kitchens
- UK police investigating allegations horsemeat was mislabelled as beef have arrested three men on suspicion of offences under the Fraud Act
- The arrests came after the FSA said on Thursday that tests had found eight horses, killed in the UK, had tested positive for the equine painkiller bute and that six may have entered the food chain in France
- On Friday, it emerged beefburgers containing horsemeat had been withdrawn from hospitals in Northern Ireland.
- The French government has accused meat processing company Spanghero of knowingly selling horsemeat labelled as beef. The firm has denied the allegations, but apologised to British consumers, saying it was "tricked as well"
- European food safety experts have met in Brussels to draw up plans to conduct DNA testing of beef products across the continent in the coming weeks
- Culture Secretary Maria Miller earlier stepped up criticism by saying retailers should not be "let off the hook" for putting wrongly labelled products on their shelves. But Labour's Mary Creagh accused ministers of being "asleep on the job"
In the letter issued on Friday, the group of food suppliers said: "We can't accept a situation where the trust customers place in us is being compromised by fraudulent activity or even as alleged, an international criminal conspiracy.
"We will do whatever it takes to restore public confidence in the food they buy and eat."
They also said they were "working around the clock" to resolve the matter.
The letter was signed by chief executive of Tesco, Philip Clarke, Asda Stores boss, Andy Clarke, the chief executive of J Sainsbury, Justin King, and Dalton Philips, chief executive of Wm Morrison Supermarkets, among others.
Supermarket chain Morrisons also responded on Twitter, saying: "Contrary to what No10 is saying, we haven't all been silent."
A spokesman told BBC News the company had carried multiple interviews and had communicated with customers. "We couldn't have been more transparent," he said.
Last month, Irish food inspectors said they had found horsemeat in beefburgers made by firms in the Irish Republic and the UK, and sold by a number of UK supermarket chains, including Tesco, Iceland, Aldi and Lidl.
Since then, a growing number of UK retailers have recalled processed beef products found to contain horse DNA.
The British Retail Consortium's Helen Dickinson told BBC Radio 4 retailers had been focusing on the swift testing of products.
Ms Dickinson added lessons must be learned by "all parts of the food industry" in the UK and Europe.
Some shops have already recalled products found to be adulterated, including Asda, which withdrew a beef Bolognese sauce on Thursday - the first fresh beef product to be involved.
Aldi, Tesco and Findus have also withdrawn some beef-based ready meals.
French food producer makes order
Comigel HQ in Metz, north-east France, asks its subsidiary, Tavola in Luxembourg, to make food products - including beef lasagne for Findus.
Factory orders meat
The Tavola factory orders the meat from Spanghero in the south of France.
Spanghero contacts a subcontractor in Cyprus to source the meat.
Subcontractor enlists trader
The Cypriot subcontractor in turn contacts a trader in the Netherlands.
Trader orders from Romania
The trader in the Netherlands places an order for meat with abattoirs in Romania.
Abattoirs send meat to France
The meat from the abattoirs travels to Spanghero in France. However, Romania rejects claims that it was responsible for wrongly describing the horsemeat from its abattoirs as beef. Horsemeat is always labelled as such, they say. The Romanian authorities claim records show orders had been for horse carcass - easily distinguishable from beef.
Meat used to make products
Spanghero sends the meat to the Comigel subsidiary’s factory in Luxembourg before the finished products are supplied to Findus and retailers across Europe, including the UK. The president of Comigel says the company was unaware the meat was coming from abroad.
Horsemeat found in Ireland and UK
Tests by Irish authorities have found equine DNA in beefburgers made by firms in the Irish Republic and the UK. Traces of horsemeat have also been found in stored meat at another plant in Ireland and one in Northern Ireland. In mainland Britain, police and officials probing alleged horsemeat mislabelling have carried out raids at a slaughterhouse in West Yorkshire and a meat firm near Aberystwyth. Three men were later arrested on suspicion of offences under the Fraud Act..