A 3-km (1.7-mile) protection zone has been put in place around the farm in Surrey, west of London, where 60 animals tested positive for the disease. A nation-wide ban on movement of all livestock has been imposed, and meat imports to the European Union suspended.
Prime Minister Gordon Brown, who cancelled his holiday and took part in a meeting of the government's Cobra emergency committee Saturday, said: "Our first priority has been to act quickly and decisively."
"I can assure people ... we are doing everything in our power to look at the scientific evidence and to get to the bottom of what has happened and then to eradicate this disease."
The infected cattle are to be culled in accordance with law. There is also a 10-km (6.2-mile) surveillance zone in Surrey where animals are monitored.
UK Chief Veterinary Officer Debby Reynolds said it was too early to predict the scale of the outbreak.
In the latest outbreak in 2001, more than six million animals were slaughtered. Damage to agriculture was estimated at over 8 billion pounds (over $16.3 billion), Brown's predecessor, Tony Blair, was strongly criticized for his handling of the situation.