An accidental leak of an experimental vaccine from a private research site was being investigated urgently Saturday night as the likely source of Britain’s foot and mouth disease outbreak. The news came as the government attempted to avert a full-scale crisis in farming and the tourism industry.

Movement of all livestock has been banned, exports to Europe stopped and country fairs cancelled to minimise the risk of the country suffering a disastrous rerun of the 2001 foot and mouth epidemic which cost the nation £8.5bn.

Scientists made a breakthrough last night as they identified the strain of the virus as one which is not naturally occurring, but is a vaccine strain, and has never been seen before in Europe. This enabled investigators to link the outbreak to a company which lies less than three miles down the road from the source of the outbreak.

Merial Animal Health, a private pharmaceutical firm shares facilities with a government lab in Pirbright, and is commissioned by the EU to formulate new vaccines for animal diseases. Both companies are expected to meet tight regulatory standards for biosecurity.

Investigators are now focusing on whether there was a lapse which meant that a batch of the vaccine, made last month, escaped the site. The company is believed to test its vaccines on animals. The virus may have been carried by the wind, or by people or vehicles down the road from the site to a rented field in the village of Normandy, near Guildford, where the outbreak happened.

By last night, dozens of vets and farm officials had been sent into a 10km “surveillance” zone around the outbreak centre at Woolfords Farm to start disinfecting equipment and vehicles, as well as testing sheep, cattle and pigs from other farms. Hundreds of cattle, sheep and pigs face slaughter amid fears that they may have been infected by an airborne strain of the virus.

US bans pork

The US Department of Agriculture has banned pork and swine products from Britain after a case of foot and mouth disease was discovered on a farm in southern England. “USDA is placing restrictions or prohibitions, depending on the type of product and level of processing, on all UK products derived from any FMD susceptible species,” a USDA official said.