Britain's Department of Environment, Food and Rural Affairs has confirmed that pigs on a farm close to the two premises infected with foot-and-mouth in Surrey are to be culled.
Defra said the decision was taken as a precautionary measure after a veterinary inspection of the animals for clinical signs of the disease proved inconclusive.
Police and trading standards officers are to patrol the protection zone around the two farms affected by the latest foot-and-mouth outbreak.
The patrols follow concerns that some people are ignoring the restrictions and tearing down signs indicating footpaths which have been closed off.
UK government vets are expected to continue their inspections on the farms, near Egham, at the centre of the outbreak.
The disease was confirmed at Hardwick Court Farm on Wednesday, only a week after the previous restrictions on cattle movements were lifted.
Earlier, Britain's Chief Veterinary Officer, Debbie Reynolds, announced a further relaxation of rules on the movement of livestock in England.
She said farmers in England would be allowed to take livestock directly to slaughter from midnight tonight.
Restrictions on movement have already been relaxed in Scotland and Wales, with many farmers in northern England arguing that they should be included as their farms are further away from the outbreaks than those of their Welsh colleagues.
The lifting of the restriction applies only to animals outside the surveillance zone currently imposed around the infected premises in Surrey.
