The foot-and-mouth epidemic is likely to persist for several months, British Agriculture Minister Mr Nick Brown has warned.
Although an exact timescale cannot be put on the outbreak, there is likely to be a long tail following the all-clear.
"It will take at least three months to wipe away residual infectivity before we can get our disease-free status back," he said.
The number of confirmed cases of foot and mouth in Britain had risen to 323.
Chief veterinary officer Mr Jim Scudamore says the outbreak is already far more severe than that in 1967.
"Just three weeks into this outbreak we are already looking at 278,000 animals affected. In the six months the 1967 outbreak lasted, only 400,000 animals were affected, which shows the severity of this," he said.
PA