Foot-and-mouth disease was feared last night to have spread to a second farm in Surrey.

A cull of more than 50 cows was ordered when animal health workers spotted at least one animal in a herd showing symptoms of the disease.

The herd was located a short distance from the research complex in Pirbright, which is suspected to be the source of the infection.

The latest animals to be culled were within a lozenge-shaped protection zone set up around the research laboratories and the farmland where the first infected cow was confirmed last Friday.

While there was dismay at the discovery of another likely infection, there was relief that it was found in an already contaminated area.

Officials from the National Farmers’ Union (NFU) had suggested privately earlier in the day that it was extremely unlikely that no more cases would be discovered.

Animal health workers who were sent into the protection zone to look for possible infections took samples from the cattle that were ordered to be culled last night.

At least one cow from the herd of more than 50 animals was suspected to be infected. If it proves to have had foot-and-mouth it will be the third animal found with the disease. The first two were found at different locations managed by the farm first affected by the outbreak. Debby Reynolds, the Chief Veterinary Officer, said after ordering the destruction of the herd last night: “I continue to urge all animal keepers to be vigilant for signs of disease and practice strict biosecurity.”

The development came as an order for 300,000 doses of vaccine against the disease was placed with the research company that is suspected of causing the outbreak. The vaccinations would be made ready for use should they be needed this week and are part of contingency plans to stop the outbreak from spreading farther.

Yesterday the European Union put Great Britain in quarantine by banning meat and milk exports from England, Scotland and Wales. The whole of mainland Britain was formally designated a high-risk area at 4pm, with all ports ordered to disinfect the wheels of every departing vehicle.

Dr Reynolds said that the decision to order the vaccinations from the research company Merial had required “careful consideration”. She refused to divulge how much the firm, which is being investigated by inspectors from the Health and Safety Executive (HSE), will be paid.

Farmers are furious that the virus may have escaped from a laboratory to infect livestock but Dr Reynolds reassured them that live viruses would not be used in the vaccine manufacturing process.

HSE inspectors have been investigating Merial’s base at Pirbright, Surrey, three miles from the first cow found to be infected. They are expected to deliver their initial report on biosecurity measures at the site at lunchtime today to Hilary Benn, the Environment Secretary.

Inspectors were also asked to investigate biosecurity at the Institute of Animal Health (IAH), the govern-ment-funded research laboratory that shares the site with Merial. The cause of the outbreak has yet to be pinpointed but a leak from the Pirbright complex is the prime suspect. The strain of virus found to have infected two cows from a Surrey farm is one employed by laboratories and was used last month by Merial and the IAH. Merial ceased all production after the infection was discovered but was given approval yesterday to produce the vaccines.

Meanwhile, David Cameron, the Tory leader, who met NFU representatives after interrupting his holiday, returned to France last night, leaving William Hague, the Shadow Foreign Secretary, in charge of his party. “Mr Cameron will be kept in close touch with the situation at all times,” a spokesman said.

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