Public sector caterers and Whitbread chain were dragged into scandal as Food Standards Agency(FSA) raided three food companies yesterday in North London and Hull Rogue to find horsemeat in British school dinners and hospital meals for the first time. FSA confirmed further police raids on three more food companies.

Tests of processed beef dishes sold in supermarkets revealed that 2% of those examined so far had found horsemeat, but as those results were being announced the scandal was confirmed to have spread to public sector caterers and major restaurant chains owned by Whitbread.

In Lancashire, northern England, cottage pies destined for 47 schools across the county were withdrawn after testing positive for horsemeat. It was not clear how long the contaminated food had been on the menu or how many pupils may have eaten it.

In Northern Ireland a range of burgers bound for hospitals were withdrawn after officials confirmed they contained equine DNA and food group Compass, which supplies more than 7,000 sites in Britain and Ireland, including schools and hospitals, said a burger product it supplied to two colleges and a small number of offices in Northern Ireland and the Republic of Ireland had tested positive.

As the horsemeat scandal continued into its sixth week, it was revealed that:

The FSA’s first wave of test results from retailers found 2% of 2,500 samples of processed beef products contained more than 1% horsemeat, though experts warned the testing “did not get to the root of the scandal”. The contaminated samples were from seven withdrawn products, including Findus lasagne and Tesco burgers. None tested positive for the drug phenylbutazone - or “bute” - used on horses but banned from the food chain.

Pub and hotel group Whitbread, which owns Premier Inn, Beefeater Grill and Brewers Fayre, confirmed horse DNA had been found in meat lasagnes and beefburgers.

The Department of health said it had written to tax-funded National Health Service (NHS) hospitals and “social care providers” asking them to carry out “suitable checking regimes on the authenticity of food”.

Sheffield council has suspended the use of all processed meat in schools and Staffordshire council said it had taken beef off school menus as a precaution.

The EU decided to start testing for the presence of unlabelled horsemeat in foods across member states. Tests will also be carried out for bute residues. In France veterinary and sanitary inspectors continued to investigate Spanghero, a meat processing and wholesale company, accused by the government of fraudulently stamping the label “beef” on 750 tonnes of cheap horsemeat.

Yesterday officials from the Food Standards Agency and police carried out three raids on suspect food companies - one in Hull and two in Tottenham, north London. A spokesman confirmed computers and documentary evidence was seized, as well as meat samples.

The raids followed the targeting of a slaughterhouse in West Yorkshire and a meat plant in Wales as part of the wider investigation. Parents in Lancashire were told cottage pies on school menus had been found to have horsemeat in them. The council said only a small number of pupils had been exposed to the food and there was no health risk.

County councillor Susie Charles said: “Relatively few schools in Lancashire use this particular product but our priority is to provide absolute assurance that meals contain what the label says; having discovered this one doesn’t, we have no hesitation in removing it from menus.” Other local authorities and catering companies who provide school food are understood to be undertaking similar tests but official testing of public sector caterers are not due until later in the spring.

The British Hospitality Association which represents many of the major providers of meals to schools said its members were testing their minced beef products in agreement with the FSA and government, although they said they were still waiting for the “vast majority” of results to come through owing to a backlog at the testing laboratories.

The Department of Health said it had written to NHS providers urging them to test all relevant food and expected the results to be made public next week.

“It’s unacceptable that anyone should have been eating meat that’s not what it says on the label,” said a spokesman. “But we would like to reassure patients that even if horsemeat is found in hospital food supplies there is nothing to suggest a safety risk to people who may have eaten the products.” Catherine Brown, the FSA’s chief executive, said the results published yesterday following tests carried out by food retailers confirmed the “overwhelming majority of beef products in this country do not contain horsemeat”.

But the results only account for about a quarter of all the products eaten by consumers and did not look for trace contamination, a decision described as “pragmatic” by the FSA. The results also did not include the positive tests uncovered by Whitbread and Compass. “Clearly, this is a fast changing picture,” said Brown, who said more test results would be revealed next Friday.

Mark Woolfe, who led the FSA’s surveillance for a decade up to 2009 said the testing did not get to the root of the scandal because the problems in the supply chain that led to the contamination in the UK were still largely unknown.

“The FSA and the industry have been remarkably silent on what went wrong in the supply chain of the companies that were found right at the start of the investigation in Ireland,” he told the Guardian. “They have had four weeks to find out. Investigating the supply chain is a much more efficient way to solve the problem than end product testing.” Last night the environment secretary, Owen Paterson, said the “food businesses” still had a lot of work to do. “They need to move quickly to complete these tests and they need to show their customers they’ve taken the right steps to make sure this doesn’t happen again.” But Mary Creagh, shadow environment secretary, said the government had repeatedly failed to get on top of the situation and ministers should order the FSA to speed up its testing.

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