Scientists were frantically trying to establish if a new outbreak of foot and mouth disease in Britain was the same virus strain as last month's cases.
Experts scrambled to determine if the two outbreaks are linked or whether the new cases are completely unrelated as officials hoped a series of clampdown measures would prevent the disease from spreading.
More animals were to be slaughtered near the site of the outbreak, southwest of London, less than a week after officials declared foot and mouth had been "eradicated" from the country and lifted restrictions.
The new case was discovered close to a farm where an outbreak was first reported last month, triggering an emergency response from the government.
Environment Secretary Hilary Benn says officials were working hard to pinpoint the exact strain in order to tailor their response.
The BBC says it understood the tests had proved the strain was the same, but a spokesman from the Department for Environment, Food and Rural Affairs (Defra) could not confirm the report.
Past incubation period
Mr Benn told BBC television: "The puzzling thing is that it is more than 30 days since the last confirmed outbreak and the incubation period of foot and mouth is two to 14 days.
"We are determined to do everything to contain and ultimately eradicate this outbreak."
Mr Benn admitted immunisation of livestock was being considered and says vaccines were ready if required.
Scotland's environment secretary Richard Lochhead told BBC radio he understood the strain was likely to be confirmed as being the same as in the August outbreak.
"At least if it's pointing in the same direction as the same strain as the previous outbreak last month, that gives us an idea that hopefully this may be contained," he says.
Experts were also waiting for test results from an unwell pig in Norfolk, eastern England, far from outbreak near London.
Defra has imposed a new England-wide ban on the movement of cattle, sheep, pigs and other ruminants following the confirmed outbreak.
Scotland and Wales followed suit.
The European Union also reimposed a ban on British meat exports to the bloc's 26 member states, the European Commission says.
Britain's red meat export market is worth about 500 million pounds (one billion dollars) a year, mostly with the EU.
Britain was the ninth largest beef exporter last year among the 27-member bloc.
Cattle were ordered slaughtered on the affected farm, near Egham, west of London.
A three-kilometre protection zone and a wider 10-kilometre surveillance zone has been thrown around the scattered farm holdings.