Britain's farmers were urged to remain watchful last night as the latest foot-and-mouth outbreak appeared to be contained.

A number of pigs within the existing protection zone, imposed around the scene of the latest outbreak, near Egham in Surrey, were culled yesterday as a precaution, said the Department for Environment, Food and Rural Affairs (Defra).

Farmers outside the wider-reaching surveillance zones are now allowed to take their animals directly for slaughter after transport restrictions were relaxed at the weekend.

A spokeswoman for Defra said: "We reiterate the message of the chief vet, Debbie Reynolds - that vigilance is still of paramount importance."

Hugh Broom, vice-chairman of the Surrey NFU (National Farmers' Union), echoed this, saying: "It's good there have been no further cases. However, we have to keep working as hard as we can to combat the disease.

"Biosecurity and vigilance with livestock remains an absolute must."

Meanwhile, scientists are investigating exactly which strain of the virus was behind the latest outbreak.

Experts have indicated that it is likely to be the same as that found in animals culled last month near Guildford.

A Health and Safety Executive inquiry found the disease may have escaped from a leaky pipe running between a Government-run Animal health laboratory and privately-run pharmaceuticals firm, Merial Animal Health, at nearby Pirbright.

In the latest outbreak, cattle which tested positive for the disease have been slaughtered at two farms within the existing 1.8-mile (3km) protection zone at Egham.

Yesterday, pigs at another farm within the zone were destroyed as a precaution.

Police and trading standards officials continued to patrol the area after a series of reported biosecurity breaches.