A cull was ordered by vets at a second farm yesterday after another cow tested positive for foot-and-mouth disease.

The slaughter resumed as those caught up in the outbreak began pointing the finger of blame, with government officials privately identifying Merial, a US-owned research company, as the likely source of infection.

Merial shares a site with the Institute for Animal Health (IAH), a government-backed research organisation that joined in the accusations against the company.

As claim and counter-claim were levelled, the protection zone designed to prevent the outbreak spreading was extended on the orders of Debby Reynolds, the Government’s Chief Veterinary Officer.

The decision was made after the second cow tested positive for the disease. It came from the same farm business as the first animal but was kept on a different site. It had shown no symptoms but samples were taken when it was culled.

The finding of the second infected cow prompted the Chief Vet to order a herd from a neighbouring farm, in Elstead, Surrey, to be culled as a precautionary measure. The first case to be identified was at Normandy, Surrey, three miles from the research complex in Pirbright. About 120 cattle from the three sites had been slaughtered last night.

National movement restrictions were in place as part of the emergency response programme put into action in an attempt to limit the spread of the disease and prevent a repeat of the £8 billion damage to the economy caused by the 2001 outbreak. The restrictions meant that agricultural shows at the weekend had to be held without livestock and all exports of live farm animals were suspended.

The bodies of the first groups of cattle to be culled were transported to an incinerator near Frome, Somerset, for destruction amid tight biosecurity to ensure that no viruses could escape into the countryside.

Gordon Brown, who is acutely aware that even if the disease is quickly contained, the costs to tourism and farming could be significant, insisted that the countryside was not closed to visitors. The Prime Minister, who broke off from his family holiday in Dorset to take charge of the response to the outbreak, urged other people not to change plans for breaks in Britain. He said: “While there is a national ban on the movement of pigs, cattle and sheep, people are free — outside the protected zone — to continue with their holidays and continue walking round the countryside.”

Investigators from the Health and Safety Executive began inspecting the site at Pirbright to establish how the virus could have escaped despite strict biosecurity measures.

The Department for Environment, Food and Rural Affairs (Defra) said that it was too early to be certain that the research complex was the source of infection, but it appeared to be the only serious candidate.

Martin Shirley, the director of the IAH, was anxious to exonerate his establishment and suggested that Merial, which produces vaccines for the disease, was to blame when he read a statement yesterday.

There remained serious questions about whether the facilities were adequate. The Conservatives pointed to a report in 2002 that identified deficiencies in infrastructure and biosecurity. The report, conducted for the Biotechnology and Biological Sciences Research Council, described facilities as substandard and said that insufficient funding had been provided by the Government.

This year Professor Shirley complained on the Farming Today programme on BBC Radio 4: “We’re trying to deliver a Rolls-Royce service for surveillance in the UK, but really we’re being funded more and more at the level of a Ford Cortina.”

David Cameron, the Conservative leader, who is meeting the National Farmers’ Union today, said that farmers would be angry if the source of the outbreak was traced back to a site under government control. “I think there are very serious questions for the Government to answer,” he said.

It was IAH scientists who originally identified the strain of the virus infecting one cow at a farm in Normandy, Surrey, after being commissioned by Defra to analyse samples from the infected cow.

Hilary Benn, the Environment Secretary, said that the link with Merial was a “promising lead”. Privately, officials said that inspectors were concentrating all their efforts on the factory. But a senior figure at the company told The Times that it shared responsibility for biosecurity on the Pirbright site with the IAH, which admitted using the same strain within the past month.

David Biland, the managing director of Merial, defended his company last night. He said: “We have been operating from this site for 15 years and during that time have produced hundreds of millions of vaccine doses. In all that time we have never had a breach in our biosecurity.” A spokesman added: “Our initial investigation shows no breach of our procedures.”

The minimum duration before any restrictions are likely to be lifted is two weeks — the length of time it takes for symptoms to develop after exposure to the disease.

Farmers within the 10km (6 miles) surveillance zone complained that they were unable to get through to Defra’s hotline and had heard nothing from the agency. Defra said that a mail drop had been carried out within the 3km zone on Saturday and that this was continuing yesterday across the 10km surveillance zone.

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