The British Ministry of Agriculture has said a suspected case of swine fever is under investigation at a pig fattening unit.
The site in Ardleigh, near Colchester, Essex, has been sealed off and officials have slapped on movement restrictions, a spokeswoman said.
British government vets have sent samples to a laboratory and expect to have the results back within nine days.
If the tests prove positive for classical swine fever, all animals at the unit will be slaughtered.
The plant is not one of those affected by the foot-and-mouth epidemic, the MAFF spokeswoman added.
"We normally get up to 12 suspected cases of classical swine fever in any one year and they all end up negative," she said.
More than 36,000 pigs were slaughtered after an outbreak of the infectious disease last August, the first in Britain for 14 years.