Farmers in Britain resumed sending animals to slaughter today after a ban on the movement of livestock to prevent foot-and-mouth from spreading was lifted in most of the country.
Cases of the disease have been found at two farms in Surrey, southern England. The government is set to confirm today whether animals culled overnight at a third farm tested positive for the disease.
Test results are also expected on the drainage system of a research laboratory near the farms as investigators search for the source of the outbreak.
The third farm under suspicion is within a protection zone set up on Friday after the first case was confirmed and is close to the two affected farms.
Outside the outbreak area, an animal-movement ban was lifted at midnight, although they were subject to strict biosecurity measures to stop the spread of the disease.
Government inspectors have said there is a "strong probability" the disease originated in two research laboratories near the infected farms and are carrying out further tests.
Both laboratories, which develop vaccines against foot-and-mouth, handle the same rare strain of the virus that has struck the Surrey herds.
The return of the disease has raised fears of a repeat of a foot-and-mouth crisis in 2001 that devastated farming and cost Britain about £8.5 billion.